Optical dielectric planar waveguide process

ABSTRACT

A method for depositing silicon oxynitride film structures is provided that is used to form planar waveguides. These film structures are deposited on substrates and the combination of the substrate and the planar waveguide is used in the formation of optical interposers and subassemblies. The silicon oxynitride film structures are deposited using low thermal budget processes and hydrogen-free oxygen and hydrogen-free nitrogen precursors to produce planar waveguides that exhibit low losses for optical signals transmitted through the waveguide of 1 dB/cm or less. The silicon oxynitride film structures and substrate exhibit low stress levels of less than 20 MPa.

This The present application is continuation of U.S. Utility patentapplication Ser. No. 16/258,292, filed on Jan. 25, 2019, entitled:“OPTICAL DIELECTRIC PLANAR WAVEGUIDE PROCESS” and continuation in-partof and claims priority from U.S. Provisional Patent Application Ser. No.62/621,659, filed on Jan. 25, 2018, entitled: “Optical DielectricInterposer”, U.S. Utility patent application Ser. No. 16/036,151, filedon Jul. 16, 2018, entitled: “Optical Dielectric Waveguide Structures”,U.S. Utility patent application Ser. No. 16/036,179, filed on Jul. 16,2018, entitled: “Methods for Optical Dielectric Waveguide Structures”,U.S. Utility patent application Ser. No. 16/036,208, filed on Jul. 16,2018, entitled: “OPTICAL DIELECTRIC WAVEGUIDE SUBASSEMBLY STRUCTURES”,U.S. Utility patent application Ser. No. 16/036,234, filed on Jul. 16,2018, entitled: “METHODS FOR OPTICAL DIELECTRIC WAVEGUIDE SUBASSEMBLYSTRUCTURE”, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to optoelectronic communication systems,and more particularly to a planar waveguide structure that is used insubmount assemblies in these systems. Optical dielectric interposers areformed from the integration and patterning of this planar waveguidestructure with a substrate to form compact interposers and opticalsubmount assemblies that provide low loss in optoelectronic packagesused for optical signal routing and transmission.

BACKGROUND

Waveguides are used in optical communication networks for thetransmission and routing of optical signals. For the transmission of theoptical signals over long distances, waveguides can take the form ofoptical fibers, thin strands of glass that are used to transfer dataover distances that can span tens of kilometers. Within the networks oflong range optical fibers are signal processing nodes that containpackaged photonic and optoelectronic circuits that are used to performvarious functions such as to encode, send, receive, decode, multiplex,and de-multiplex, among other optical and electrical signal processingfunctions, the optical signals that are delivered to these processingnodes via the optical fibers. And within the optoelectronic circuits inthese processing nodes, optical signals are transmitted via free spaceand through short lengths of waveguide. These short lengths of waveguideare used to guide signals to a variety of small packaged devices orcomponents that can transfer, combine, split, and route optical signalsas the demands of the network require.

Optoelectronic packages at signal processing nodes in opticalcommunications networks generally include an optical submount assembly,which typically consists of one or more optical die (such as lasers andphotodetectors), and that can include either the means for the freespace transmission of optical signals or the planar waveguides andassociated optical routing components, all of which are enclosed in anhermetically-sealed cavity formed by a cap and a substrate. A submountassembly can include, for example. a substrate or interposer, theoptical routing components, and the signal-generating andsignal-receiving devices and components.

Routing of optical signals from the optical fibers to components on thesubmount assembly have historically been accomplished via transmissionin free space, and to some extent, via planar optical waveguides on thesubmount assembly. Optical transmission in free space can require lensesto focus and direct the optical signals between components in theoptical circuits and can require large spatial volumes to accommodatethese lenses. The large spatial volumes can lead to undesirably largepackage sizes for these optical circuits. Additionally, the transmissionof the signals in free space can result in significant signal lossesfrom uncontrolled scattering and reflection.

Currently, the capability for fabricating planar waveguide structures ofsufficient thickness with low stress is limited, and therefore, a needexists in the art of optoelectronic packaging for a planar waveguidestructure that can be deposited onto a substrate, and from which compactand economical interposers and submount assemblies can be formed. Thus,there is a need in the art for a method to produce compact, planaroptical waveguide structures that exhibit low optical loss withoutdeformation of the underlying substrate.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of systems,methods, and other aspects of the invention. It will be apparent to aperson skilled in the art that the illustrated element boundaries (e.g.,boxes, groups of boxes, or other shapes) in the figures represent oneexample of the boundaries. In some examples, one element may be designedas multiple elements, or multiple elements may be designed as oneelement. In some examples, an element shown as an internal component ofone element may be implemented as an external component in another, andvice versa.

Various embodiments of the present invention are illustrated by way ofexample, and not limited by the appended figures, in which likereferences indicate similar elements, and in which:

FIG. 1A-1C show cross-sectional schematic views of the inventivedielectric film structure for the formation of integrated planarwaveguide structures: FIG. 1A a cross-sectional view of a single ormultilayer dielectric top spacer layer structure for the inventiveplanar dielectric waveguide structure; FIG. 1B a cross-sectional view ofa multilayer, repeating silicon oxynitride film structure for theinventive planar dielectric waveguide structure; and FIG. 1C across-sectional view of a single or multilayer dielectric bottom spacerlayer structure for the inventive planar dielectric waveguide structure;

FIG. 2A-2B show measured film stress in accordance with embodiments forFIG. 2A dielectric films deposited at various film thicknesses, and FIG.2B dielectric films of various refractive indexes;

FIG. 3A-3B show measured optical losses in accordance with embodimentsfor FIG. 3A dielectric films of various refractive indexes and FIG. 3Bdielectric waveguide film structures with various bottom buffer layerfilm thicknesses;

FIG. 4A-4C show steps for forming some embodiments of the inventivedielectric film structure FIG. 4A at low temperature and having lowstress and low optical loss, FIG. 4B with each dielectric film depositedat low temperature and having low stress and low optical loss, and FIG.4C that include a substrate with a buffer layer, one or more optionalbottom spacer layers, a repeating stack of one or more dielectriclayers, one or more optional top spacer layers, and an optional toplayer, followed by pattering of the stack to form a waveguide;

FIG. 5 shows a schematic of a typical plasma enhanced chemical vapordeposition system;

FIG. 6 shows the measured refractive index for waveguide structures thatwere deposited over a range of the silicon-containing precursor gasflow;

FIG. 7A-7B show cross sectional schematic views of embodiments of anintegrated planar waveguide on a substrate: FIG. 7A withoutoptical/electrical devices, and FIG. 7B with optical/electrical devices;

FIG. 8A-8B show cross sectional schematic views of embodiments ofintegrated planar waveguides on a substrate with an interconnect layerin accordance with the inventive process: FIG. 8A withoutoptical/electrical devices and FIG. 8B with optical/electrical devices;

FIG. 9A-9B show cross sectional schematic views of embodiments ofintegrated planar waveguides on a substrate with interconnect layer andintegrated electrical devices in the substrate in accordance with theinventive process: FIG. 9A without surface mounted optical or electricaldevices and FIG. 9B with surface mounted optical or electrical device;

FIG. 10A-10B show cross sectional schematic views of embodiments ofintegrated planar waveguides on a substrate with interconnect layer andintegrated electrical devices in the substrate in accordance with theinventive process shown with interconnections between top surfacemounted device and integrated electrical devices in the substrate: FIG.10A shown without the top mounted optical or electrical devices inplace, and FIG. 10B with top mounted optical or electrical device; alsoshown is the position of an optical fiber relative to the planarwaveguide in an embodiment;

FIG. 11A-11D show cross sectional schematic views of embodiments of asubstrate with interconnect layer: FIG. 11A with inventive dielectricstack mounted via bond pads to the substrate as a discrete opticalwaveguide component, FIG. 11B with inventive dielectric stack mounted tothe substrate as a discrete optical waveguide component and aligned withdiscrete optical and electrical devices, and aligned to an opticalfiber, FIG. 11C with inventive dielectric stack mounted to the substrateas a discrete optical waveguide component, for which the substratecontains integrated electrical devices, and FIG. 11D with inventivedielectric stack mounted to the substrate as a discrete opticalwaveguide component and aligned with discrete optical and electricaldevices, and aligned to an optical fiber for an embodiment in which thesubstrate contains integrated electrical devices;

FIG. 12A-12B show steps in the fabrication of embodiments of providing apatterned dielectric waveguide structure FIG. 12A on a substrate withone or more integrated devices in the substrate that are coupled to aninterconnect layer, and FIG. 12B on a substrate with one or moreintegrated devices in the substrate that are coupled to the inventiveplanar waveguide through an interconnect layer and a device, and to anoptical fiber that is configured to interface with the planar waveguide;

FIG. 13A shows a perspective schematic view of a substrate withpatterned inventive dielectric waveguide structure, with a v-groove formounting and alignment of an optical fiber and with mechanical stops forthe mounting and alignment of optical and electrical devices and die,and FIG. 13B shows a cross sectional schematic view of embodiments ofintegrated planar waveguide structures on a substrate with alignmentmark and stops for alignment of optical/electrical devices;

FIG. 14 shows steps in the fabrication of embodiments of the inventivedielectric film structures for providing patterned dielectric waveguideson substrates with features for the alignment of optical and electricaldevices;

FIG. 15A-15B show cross sectional schematic views of embodiments ofintegrated planar waveguides on a substrate with integrated heat sinklayer FIG. 15A on the substrate, and FIG. 15B within the interconnectlayer;

FIGS. 16A-16B show steps in the fabrication of embodiments of theinventive dielectric film structure for providing patterned dielectricwaveguide structures with FIG. 16A interconnection layer formed on athermal conductive layer, and FIG. 16B a high thermal conductivitydielectric layer within the interconnect layer;

FIG. 17A-17D show a cross sectional schematic view of embodiments ofintegrated planar waveguides on a substrate shown FIG. 17A withunpatterned dielectric waveguide stack, FIG. 17B patterned dielectricwaveguide structure with resulting cavity shown in cross section and, inthe inset, in a perspective view, FIG. 17C with patterned dielectricwaveguide structure and with mounted optical/electrical die within thecavity, and FIG. 17D with patterned dielectric waveguide structure,mounted optical/electrical die, and hermetic sealing cap;

FIG. 18 shows steps in the fabrication of embodiments of the inventivedielectric film structure for the formation of integrated planarwaveguides and mechanical support structures to support hermeticsealing.

SUMMARY

Embodiments of the present invention are directed to the fabrication ofintegrated planar dielectric waveguides that are formed and patterned onsubstrates. The combination of an integrated planar waveguide and asubstrate, to form an optical dielectric interposer, serves as asubcomponent of an optical submount assembly for an optoelectronicpackage. Optical losses in dielectric waveguides are minimized with theuse of nitrogen and oxygen precursors that do not contain hydrogen.

The present invention is based, in part, on the development of adielectric waveguide structure that transmits optical signals with lowloss, is integrated into a substrate and thereby reduces fabricationcosts, is deposited at low processing temperatures of less than 400° C.,and preferably less than or at approximately 300° C., and is fabricatedwith low stress to prevent stress-induced delamination of the filmstructure and deformation of the substrate. The inventive structure andmethod for producing the structure enables the fabrication of waveguidesover a wide range of thicknesses up to 20 micrometers and greater. Thebenefits of this capability, as further described herein, providesuperior optical and mechanical performance and superior economicbenefits in comparison to the current state of the art.

Waveguides that are fabricated using the inventive techniques describedherein, have low residual stresses and thus very thick layeredstructures can be deposited. The thicker, multilayer waveguidestructures obtainable with the inventive method, coupled with lowresidual hydrogen concentrations in the deposited layers, allow for lowoptical loss. Further, the thick waveguides obtainable with theinventive method are provided at a thermal budget and can thus befabricated on substrates that contain metallization layers andintegrated electrical and optoelectrical devices.

DETAILED DESCRIPTION

The ensuing description provides exemplary embodiment(s) only, and isnot intended to limit the scope, applicability or configuration of thedisclosure. Rather, the ensuing description of the exemplaryembodiment(s) will provide those skilled in the art with an enablingdescription for implementing an exemplary embodiment. It beingunderstood that various changes may be made in the function andarrangement of elements without departing from the spirit and scope asset forth in the appended claims.

An “interposer” as used herein and throughout this disclosure refers to,but is not limited to, a substrate that provides mechanical support andelectrical or optical interface routing from one or more electrical,optical, and optoelectrical devices to another. Interposers aretypically used to route optical or electrical connections from variousdevices or die that are mounted on, or connected to, the interposer. An“optical interposer” is an interposer that provides for the opticalinterfacing between optical devices mounted or connected thereon.

A “submount assembly” as used herein and throughout this disclosurerefers to, but is not limited to, an assembly that includes a substrate,typically an interposer, that is populated with one or more optical,optoelectrical, and electrical devices.

A “substrate” as used herein and throughout this disclosure refers to,but is not limited to, a mechanical support upon which an interposer isformed. Substrates may include, but not be limited to, silicon, indiumphosphide, gallium arsenide, silicon, silicon oxide-on-silicon, silicondioxide-on-silicon, silica-on-polymer, glass, a metal, a ceramic, apolymer, or a combination thereof. Substrates may include asemiconductor or other substrate material, and one or more layers ofmaterials such as those used in the formation of an interconnect layer.

An “optical die” as used herein and throughout this disclosure refersto, but is not limited to, a discrete optical device such as a laser orphotodetector that can be positioned into a submount assembly as acomponent of an optical or optoelectronic circuit.

An “optoelectronic package” as used herein and throughout thisdisclosure refers to, but is not limited to, an assembly that istypically hermetically sealed, and that typically includes a submountassembly and a cap; the package typically provides electrical, optical,or both electrical and optical interconnects for combining with externaloptoelectronic, electronic, and optical components as in, for example,an optical communications network, an optical circuit, or an electricalcircuit.

An “optical waveguide” as used herein and throughout this disclosurerefers to, but is not limited to, a medium for transmitting opticalsignals.

“Optical signals” as used herein and throughout this disclosure refersto, but is not limited to, electromagnetic signals typically in theinfrared and visible light ranges of the electromagnetic spectrum thatare encoded with information.

A “semiconductor” as used herein and throughout this disclosure refersto, but is not limited to, a material having an electrical conductivityvalue falling between that of a conductor and an insulator. The materialmay be an elemental material or a compound material. A semiconductor mayinclude, but not be limited to, an element, a binary alloy, a tertiaryalloy, and a quaternary alloy. Structures formed using a semiconductoror semiconductors may include a single semiconductor material, two ormore semiconductor materials, a semiconductor alloy of a singlecomposition, a semiconductor alloy of two or more discrete compositions,and a semiconductor alloy graded from a first semiconductor alloy to asecond semiconductor alloy. A semiconductor may be one of undoped(intrinsic), p-type doped, n-typed doped, graded in doping from a firstdoping level of one type to a second doping level of the same type, andgraded in doping from a first doping level of one type to a seconddoping level of a different type. Semiconductors may include, but arenot limited to III-V semiconductors, such as those between aluminum(Al), gallium (Ga), and indium (In) with nitrogen (N), phosphorous (P),arsenic (As) and tin (Sb), including for example GaN, GaP, GaAs, InP,InAs, AN and AlAs.

“Silicon oxynitride” as used herein and throughout this disclosurerefers to, but is not limited to, a dielectric material that is formedby a combination of constituent elements of silicon, oxygen, andnitrogen. In some instances, the term “silicon oxynitride” can refer tosilicon oxides and silicon nitrides in the general sense that siliconoxides and silicon nitrides are silicon oxynitrides with very low orinsignificant levels of either the nitrogen in the case of siliconoxides, and oxygen in the case of silicon nitrides. Film properties,such as the refractive index, can be controlled or varied by varying theconcentrations and the ratios of the constituent elements of silicon,oxygen, and nitrogen, and to some extent, by the concentrations ofimpurities in the films. The removal of nitrogen or the reduction ofnitrogen to low levels, for example, in one film of a film stack, doesnot change the designation of the material as silicon oxynitride withinthe context of this disclosure. Similarly, the removal of oxygen or thereduction of oxygen to very low levels does not change the designationof the resulting material as a silicon oxynitride. Materials with low orunmeasurable levels of either nitrogen or oxygen should, therefore, beviewed as silicon oxynitrides within the context of this disclosure. Theratio of silicon to oxygen to nitrogen in silicon oxynitride films canvary over a wide range and variations in the ratio of these constituentelements can lead to variations in the refractive indices of siliconoxynitride films as described herein. The concentrations of impuritiesin the films, from the deposition processes used to form the films, canalso influence the indices of refraction of the silicon oxynitridefilms. Silicon oxynitride is electrically insulating and opticallytransparent.

“Silicon oxide” as used herein and throughout this disclosure refers to,but is not limited to, a dielectric material that is formed from acombination of silicon and oxygen, and in some instances may containother elements such as hydrogen, for example, as a byproduct of thedeposition method. In its most common form, the ratio of oxygen tosilicon is 2:1 (silicon dioxide) but variations in this ratio remainwithin the scope of the definition of silicon oxide as used for thesilicon oxide films in this disclosure. Similarly, variations instoichiometry are to be anticipated and applicable for filmsspecifically referred to in this disclosure as silicon dioxide.

“Silicon nitride” as used herein and throughout this disclosure refersto, but is not limited to, a dielectric material that is formed from acombination of silicon and nitrogen, and in some instances may containother elements such as hydrogen, for example, as a byproduct of thedeposition method. In its most common form, the ratio of nitrogen tosilicon is 4:3, but variations in this ratio remain within the scope ofthe definition of silicon nitride as used for the silicon nitride filmsin this disclosure.

A “metal” as used herein and throughout this disclosure refers to, butis not limited to, a material (element, compound, and alloy) that hasgood electrical and thermal conductivity. This may include, but not belimited to, gold, chromium, aluminum, silver, platinum, nickel, copper,rhodium, palladium, tungsten, and combinations of such materials.

An “electrode”, “contact”, “track”, “trace”, or “terminal” as usedherein and throughout this disclosure refers to, but is not limited to,a material having good electrical conductivity and that is typically,optically opaque. This includes structures formed from thin films, thickfilms, and plated films for example of materials including, but notlimited to, metals such as gold, chromium, aluminum, silver, platinum,nickel, copper, rhodium, palladium, tungsten, and combinations of suchmaterials. Other electrode configurations may employ combinations ofmetals, for example, a chromium adhesion layer and a gold electrodelayer.

A “precursor” as used herein and throughout this disclosure is amaterial in gaseous or vapor form that contains one or more of theconstituent elements of a material targeted for deposition. Molecularsilane (SiH₄), for example, contains elements of silicon and hydrogen,and is a widely used precursor for depositing films in chemical vapordeposition processes, for example, that contain silicon (such assilicon, silicon dioxide, silicon nitride, silicon oxynitride, etc.)Deposition of films such as silicon dioxide, for example, requires atleast a second precursor to provide the oxygen in applications in whichsilane is used since the silane does not contain oxygen. Molecularoxygen (O₂) is often used as a precursor with silane in the depositionof thin films of silicon dioxide to provide the oxygen atoms requiredfor the silicon oxide formation. It is important to note that not all ofthe elements contained in the precursor or precursors are required ordesired in the deposited films. In the case of silane, for example, whenused as a precursor to deposit thin films of silicon dioxide, residualhydrogen can lead to a reduction in the quality of the films relative tostoichiometrically pure films without the hydrogen.

References to “an embodiment”, “another embodiment”, “yet anotherembodiment”, “one example”, “another example”, “yet another example”,“for example” and so on, indicate that the embodiment(s) or example(s)so described may include a particular feature, structure,characteristic, property, element, or limitation, but that not everyembodiment or example necessarily includes that particular feature,structure, characteristic, property, element or limitation. Furthermore,repeated use of the phrase “in an embodiment” does not necessarily referto the same embodiment.

Planar optical waveguides that can be fabricated on substrates, and thatcan further be utilized in the formation of interposers, and ultimatelyin submount assemblies, offer the potential for significant reduction infabrication complexity and in optoelectronic package sizes over currentmethods. The integration and patterning of planar waveguide structureson substrates allow for the transmission and distribution of opticalsignals within the subassemblies, which can eliminate or reduce therequirements to mount discrete optical components to the subassembly.Integrated waveguide structures also allow for the formation of opticaldevice structures, such as filters, gratings, and spot size converters,for example, directly onto the substrate of the interposer or submountassembly, the integration of which can lead to significant costadvantages. Further, the ability to pattern and integrate planarwaveguide structures on substrates that contain metal interconnectlayers enables the use of integrated optoelectrical devices with theplanar waveguides and the planar waveguide device structures fabricatedon the substrates. This combination of integrated optical componentswith electrical interconnect layers requires low thermal budgetfabrication processes so as to not damage the interconnect layerspresent in the substrates or interposers upon which the planarwaveguides are fabricated.

In an embodiment, a method for depositing a planar dielectric layer ofsilicon oxynitride on a substrate is provided which includes maintainingthe substrate at a predetermined temperature and exposing the substratesurface to a plasma enhanced chemical vapor deposition processcontaining a silicon-containing precursor gas that may or may notcontain hydrogen, a nitrogen-containing precursor that does not includehydrogen, and an oxygen-containing precursor that does not containhydrogen. Advantages of the inventive low thermal budget process forforming the inventive dielectric waveguide structure 140 includepredetermined temperatures that are sufficiently low to allow forsubstrates with metallization layers that would otherwise not beimplementable with higher thermal budget processes.

In general, the thermal budget of a manufacturing process is the totalamount of thermal energy that is transferred to the substrate during anoperation that is performed at elevated temperature, and is proportionalto the temperature and duration of each of the steps in the given hightemperature process. Lower temperature processes can typically withstandmuch longer durations without deleteriously impacting the substrate orfeatures of the substrate that were formed in prior processes.Additionally, lower temperature processes in general, and morespecifically, lower thermal budget processes, allow for features to beincorporated into the substrate that would not otherwise be available incases in which high thermal budget processes are required. In thepresent inventive process and method, low thermal budget processingprovides advantages in the formation of dielectric film structures thatinclude 1) a reduction in the potential for deformation of thesubstrates, and 2) the capability to incorporate integrated electricaldevices and metallized layers into the substrate prior to thefabrication of the planar waveguide structures. High thermal budgetprocesses in which the substrates are subjected to high temperatures,even for short durations, can lead to warpage and other forms ofdeformation of the substrate. Additionally, integrated electricaldevices and metallization layers might also be subject to damage byprocesses at higher thermal budgets or require more robust andpotentially more expensive processing to reduce this potential fordamage. It is therefore advantageous for deposition processes for planarwaveguide structures to have sufficiently low thermal budgets so as tonot result in deformation or warping of the substrate, and so as not toresult in damage to integrated electrical devices or metallized layersthat are formed on the substrate prior to the formation of thewaveguides. Additionally, the use of low thermal budget processes allowsfor the use of more economically favorable materials and processingtechniques that may not have the robustness to withstand higher thermalbudget processes. In the case of material selection, for example, theuse of low thermal budget processes can allow for a variety of polymericmaterials to be utilized that are commonly implemented in semiconductorfabrication schemes that would otherwise not withstand exposure to hightemperature, or high thermal budget processes. Similarly, othermaterials and combinations of materials can be utilized with low thermalbudget fabrication schemes that are susceptible to damage upon exposureto higher thermal budget processes.

In applications in which electrical devices or metallization layers areincorporated into the substrate, low thermal budget processes offersignificantly greater levels of flexibility in processing over higherthermal budget processes. In integrated device structures, themetallization layers are typically the most susceptible to theintroduction of damage from high thermal budget processes, althoughother aspects of the device might also be affected by excursions to hightemperatures.

A metallized layer structure in or on a substrate typically consists ofone or more patterned metal layers that are insulated with one or morelayers of dielectric material to electrically isolate the metal layers.For example, a metallization layer structure can consist of multiplelayers of patterned aluminum, copper, or other metals, or a combinationof metals that are encapsulated within a dielectric material such assilicon dioxide, silicon nitride, a polymer, or other insulatingmaterial that provides electrical isolation between traces formed by themetal layers. The metallized layers with the dielectric insulationlayers can be fabricated using either subtractive processing such asmetal deposition followed by an etching step to pattern the metal layersor additive processing, such as damascene and dual-damascene processingin which dielectric intermetal layers are patterned, etched, and thenfilled with metal to form the metal traces that are subsequently used tointerconnect devices that will ultimately be positioned or fabricated onthe substrate. In the case of aluminum and alloys of aluminum,subtractive processes are most commonly used in which an aluminum layeris deposited, patterned, and etched to form a patterned metalinterconnect layer and then covered with a dielectric to electricallyisolate and protect, among other important aspects, the traces createdin the aluminum layer. Conversely, in the case of copper metallization,damascene processes are most commonly used. In a damascene process, adielectric layer is deposited, patterned, and etched to form trenchesthat are subsequently filled with copper to form the metal interconnecttraces. The copper-filled dielectric structures are then subjected to aplanarization step to remove excess copper and then capped with adielectric layer to isolate and protect the copper layer below. For boththe subtractive and additive processes, the steps are repeated forapplications in which multiple metal layers are implemented in thestructure. In cases in which multiple layers of metal are required,allowance must be made to vertically interconnect the metal layers asrequired by the circuit design. This overview of forming metallizationlayer structures is a simplified overview but nonetheless highlightssome of the key aspects of metallization layer formation that can beused to form the metallization layer on a substrate prior to theformation of the inventive planar dielectric waveguide structure. Theformation of metallization layers using either subtractive or additiveprocesses are well known in the art of integrated circuit manufacturingand applicable to the formation of metallization layers on substratesused to form optoelectronic interposers and subassemblies.

The ultimate temperature for a substrate with one or more metal layers,in the extreme case, is limited by the melting point temperature for themetal, although other deleterious effects are often observed attemperatures much lower than the melting temperature for the metal. Forapplications in which metallization layers utilize aluminum, the meltingpoint for which is approximately 660° C., low thermal budget processesare particularly enabling due to the susceptibility of the aluminum toreflow at temperatures much lower than the melting point. The reductionin appearance of other effects in addition to metal reflow, such as voidformation, diffusion, and alloying with adjacent materials, for example,among other potential damage mechanisms are also minimized using lowerthermal budget processes.

In an embodiment, a method for depositing a planar dielectric layer ofsilicon oxynitride on a substrate is provided which includes maintainingthe substrate at a predetermined temperature of less than 500 C andexposing the substrate surface to a plasma enhanced chemical vapordeposition process containing a silicon-containing precursor gas thatmay or may not contain hydrogen, a nitrogen-containing precursor thatdoes not include hydrogen, and an oxygen-containing precursor that doesnot contain hydrogen. In another embodiment, a method for depositing aplanar dielectric layer of silicon oxynitride on a substrate is providedwhich includes maintaining the substrate at a predetermined temperatureof less than 400 C and exposing the substrate surface to a plasmaenhanced chemical vapor deposition process containing asilicon-containing precursor gas that may or may not contain hydrogen, anitrogen-containing precursor that does not include hydrogen, and anoxygen-containing precursor that does not contain hydrogen. And in yetanother embodiment, a method for depositing a planar dielectric layer ofsilicon oxynitride on a substrate is provided which includes maintainingthe substrate at a predetermined temperature of less than orapproximately equal to 300 C and exposing the substrate surface to aplasma enhanced chemical vapor deposition process containing asilicon-containing precursor gas that may or may not contain hydrogen, anitrogen-containing precursor that does not include hydrogen, and anoxygen-containing precursor that does not contain hydrogen. Inembodiments, low thermal budget film deposition processes, as describedherein, are used to form low stress film structures as shown in FIG. 1for dielectric film structure 140.

Thick dielectric films of greater than a few micrometers for use aswaveguides can provide transmission and routing pathways with desirablylow levels of optical signal attenuation. Optical absorption isminimized in the current invention with the use of hydrogen-freeprecursors for oxygen and nitrogen that produce low levels ofnitrogen-hydrogen bonding in deposited films, and when combined with thelow stress levels of these deposited films, enable thick film structuresas described in this disclosure to be fabricated. A low concentration ofresidual hydrogen-nitrogen bonding in the as-deposited films with theuse of the hydrogen-free precursors provides the desirably low levels ofoptical absorption with a low thermal budget deposition method, and themeans for deposited relatively thick dielectric layers that are low instress. Thus, the inventive method provides a means for producing thickdielectric films that have low stress, low optical absorption, and thatare fabricated with low thermal budget processes.

Optical and electrical devices that are fabricated in, and utilizedwith, dielectric interposer layers that are formed with a low thermalbudget enable a wide range of substrate functionality and integration.Integrated dielectric waveguides in dielectric interposers, for example,that can be fabricated with low stress and with low optical loss, allowfor increased levels of integration. Low stress levels allow for minimalsubstrate deformation particularly in thin substrates. Low optical lossallows for higher density components and smaller overall package sizesfor submount assemblies. Additionally, dielectric interposers that canbe deposited at temperatures that do not lead to degradation oftemperature sensitive metallization layers allow for the fabrication ofwaveguides on substrates that include metallization. Substrates thatcontain integrated metallization layers includes a wide range of opticaldevice assemblies that require electrical contact layers to interconnectoptoelectrical devices to one another within the submount assembly, todevices within the substrate, and to other assemblies connected to thesubmount assembly. The ability to fabricate integrated waveguides onmetalized CMOS structures, for example, enables an expansive range offunctionality and applications in integrated communications technology.

In exemplary embodiments, planar dielectric film structures of multiplelayers of silicon oxynitride are formed on a substrate and patternedinto waveguides using hydrogen-free precursors for the nitrogen andoxygen components of the deposited silicon oxynitride. The inventiveprocesses can produce patterned waveguides on substrates with opticallosses that are typically less than 1 dB/cm and that exhibitpost-deposition stress levels of less than 20 MPa. The inventiveprocesses in embodiments use plasma enhanced chemical vapor deposition(PECVD) with process chemistries that do not utilize hydrogen-containingnitrogen and oxygen precursors. Residual hydrogen in silicon oxynitridefilms has been linked to high levels of loss for optical signalstransmitted through waveguides fabricated from silicon oxynitridereportedly due to the formation of high levels of nitrogen-hydrogenbonds in the deposited films. Nitrogen-hydrogen bonds in deposited filmsare known to absorb optical signals at wavelengths commonly used inoptical fiber communication networks. In the inventive process, theincorporation of the hydrogen, and the formation of thenitrogen-hydrogen bonds, is limited in the deposited films by the use ofnitrogen and oxygen precursor gases that do not contain hydrogen. Theinventive process and method, therefore, provide a preferred approach toforming low loss optical waveguide structures by combining a dielectricstack structure and a low thermal budget process that minimizesnitrogen-hydrogen bonds in the silicon oxynitride. The low thermalbudget process utilizes non-hydrogen-containing nitrogen and oxygenprecursors during the dielectric film deposition to provide waveguidesthat exhibit low optical signal loss.

Although the use of hydrogen-free precursors in the inventive dielectricfilm deposition process for the formation of the inventive filmstructure can result in significantly lower film deposition ratesrelative to processes that utilize hydrogen-containing precursors, thecombination of the inventive process with these film structures enable arange of innovations as a result of the reductions in optical signalloss and residual stresses in the deposited films. The use ofhydrogen-free nitrogen precursors and hydrogen-free oxygen precursorsgreatly reduces the formation of nitrogen-hydrogen bonds in thedeposited silicon oxynitride films, and therefore, significantly reducesthe absorption of optical signals in waveguides fabricated from thesefilms in comparison to processes that utilize hydrogen-containingprecursors.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided herein. It should beunderstood that the detailed description of exemplary embodiments isintended for illustration purposes only and is, therefore, not intendedto necessarily limit the scope of the present invention.

An embodiment of the inventive dielectric waveguide structure is shownin FIG. 1. The inventive dielectric waveguide structure is a stack ofdielectric films deposited on a substrate 110 to form optical dielectricinterposer 100. In an embodiment, the substrate is silicon. In otherembodiments, the substrate is GaAs, InP, SiGe, SiC, or anothersemiconductor. In yet other embodiments, the substrate is aluminumnitride, aluminum oxide, silicon dioxide, quartz, glass, sapphire, oranother ceramic or dielectric material. In yet other embodiments, thesubstrate is a metal. And in yet other embodiments, the substrate is alayered structure of one or more of a semiconductor, a ceramic, and ametal. It is to be understood that the substrate can be any materialthat provides a suitable mechanical support. It is to be furtherunderstood that a substrate with an interconnect layer that containselectrical lines and traces, separated with intermetal dielectricmaterial, is a substrate.

The optical dielectric interposer 100 includes a planar waveguidestructure formed on substrate 110. In the preferred embodiment, theplanar waveguide structure includes a buffer layer 130, spacer layer138, a repeating stack of silicon oxynitride films 142, a top spacerlayer 150, and an optional top layer 158.

In preferred embodiments, buffer layer 130 is one or more layers ofsilicon dioxide or silicon oxynitride. In some embodiments, the bufferlayer is a layer of silicon oxynitride. In a preferred embodiment, thebuffer layer 130 is a silicon oxynitride layer, 5000 nm in thickness,with an index of refraction of 1.55. In other embodiments, the bufferlayer 130 is silicon oxynitride with refractive index of 1.55 and isthicker than 2000 nm. In other embodiments, the buffer layer 130 is asilicon dioxide layer with a refractive index of approximately 1.445. Inother embodiments, the buffer layer 130 is a silicon dioxide layer witha refractive index of approximately 1.445 that is greater than 2000 nmin thickness. In a preferred embodiment, the buffer layer 130 is asilicon dioxide layer that is approximately 4000 nm in thickness andwith a refractive index of approximately 1.445.

Buffer layer 130 can be a composite layer of one or more layers ofsilicon dioxide or silicon oxynitride with varying thicknesses that insome embodiments sum to greater than 4000 nm in total thickness.Similarly, the buffer layer 130, in some preferred embodiments, can be acomposite layer of one or more layers with varying refractive index,that when combined, provide a total thickness of greater than 4000 nmand a composite refractive index in the range of 1.4 to 2.02.

In preferred embodiments, spacer layer 138 is one or more layers ofsilicon dioxide or silicon oxynitride. In a preferred embodiment, thespacer layer 138 is a single spacer layer 138 a of silicon oxynitride,500 nm in thickness, with an index of refraction of 1.55. In someembodiments, single spacer layer 138 a is a layer of a single material,such as silicon dioxide. In other preferred embodiments, single spacerlayer 138 a is a layer of silicon oxynitride. In yet other preferredembodiments, the single spacer layer 138 a is a layer of siliconoxynitride with refractive index of 1.55 with thickness of 500 nm. Inyet other embodiments, single spacer layer 138 a is a layer of siliconoxynitride with thickness in the range of 0 to 1000 nm. Although inpreferred embodiments, a spacer layer 138 is included in the structure,in some other embodiments, the spacer layer 138, can be combined withthe buffer layer, can be made very thin, or is not included (FIG. 1C).

Spacer layer 138 can be a composite spacer layer 138 b of one or morelayers of silicon oxynitride or silicon dioxide. In an embodiment,composite spacer layer 138 b is includes two layers of siliconoxynitride with thicknesses of 250 nm and with a composite refractiveindex of approximately 1.55. In some embodiments, the sum of thethicknesses of the two layers in composite spacer layer 138 b is in therange of 1 to 1000 nm (FIG. 1C).

Similarly, the spacer layer 138 can be a composite layer 138 c of threeor more layers with the same or varying thicknesses and refractiveindices, that when combined, provide a total thickness in the range of 1nm to 1000 nm and a composite refractive index in the range of 1.4 to2.02 (FIG. 1C).

The combined thicknesses of the buffer layer 130 and the spacer layer138 in embodiments provide spatial separation between the core repeatingstack 142 and the substrate 110 and reduce, minimize, or eliminate theinteraction of the transmitted optical signal with the substrate 110.The transmission of optical signals with low optical loss through therepeating structure 142 requires some degree of confinement of thesignal to the waveguide with minimal interaction of the optical signalswith the substrate 110 in embodiments for which the optical signals areattenuated in the substrate material. Silicon and some othersemiconductors, and metal layers in the interconnect layers, forexample, can lead to significant attenuation of optical signals. Thecombined thicknesses of the buffer layer 130 and the spacer 138 providespatial isolation between the substrate materials and the upper layersof the inventive dielectric stack structure to reduce the interaction oftransmitted optical signals with materials in the substrate that canlead to attenuation.

Dielectric stack 142 forms the core of the inventive waveguide structurethrough which optical signals can be transmitted with low optical loss.In preferred embodiments, the dielectric film stack 142 of is a layeredstructure of silicon oxynitride films.

In an embodiment, the dielectric stack 142 has a repeating stack 142 aof two dielectric films in which the constituent films within therepeating stack structure 142 a are of differing refractive indices.Differences in the refractive indices can occur primarily from changesin the stoichiometric composition of the films. In preferredembodiments, the changes in the stoichiometry of the films in therepeating film structure 142 is accomplished with changes in the processconditions used in the deposition of the films in the repeating filmstructure 142. In a preferred embodiment, the repeating stack structure142 a includes a first film 143 of 900 nm of silicon oxynitride with anindex of refraction of 1.6 and a second film 144 of 50 nm of siliconoxynitride with an index of refraction of 1.7. In another preferredembodiment, the repeating structure 142 a includes a first film 143 of40 nm of silicon oxynitride with an index of refraction of 1.7 and asecond film 144 of 500 nm of silicon oxynitride with an index ofrefraction of 1.65. In yet another preferred embodiment, the repeatingstructure 142 a includes a first film 143 of 60 nm of silicon oxynitridewith an index of refraction of 1.7 and a second film 144 of 500 nm ofsilicon oxynitride with an index of refraction of 1.65. It is to beunderstood that the order of the first film 143 and the second film 144in embodiments can be reversed and remain within the scope and spirit ofthe invention (FIG. 1B).

In another embodiment, the dielectric stack 142 b has a repeating stack142 of more than two dielectric films in which the constituent films145-147 within the repeating structure 142 a are of differing refractiveindices, and in some embodiments, of the same or differing thicknesses.In an embodiment, repeating stack 142 b includes a first film 145 of 400nm of silicon oxynitride with an index of refraction of 1.6, a secondfilm 146 of 500 nm of silicon oxynitride with an index of refraction of1.65, and a third film 147 of 50 nm of silicon oxynitride with an indexof refraction of 1.7 (FIG. 1B).

In yet other embodiments, the repeating stack 142 c of dielectric stack142 includes more than three layers for which the index of refractionfor the constituent layers of silicon oxynitride is varied to achievethe total film thickness of the overall dielectric stack structure 142.In embodiments, for example, in which the repeating film structure 142 ahas two constituent films with a combined thickness of 600 nm, the stackmust be repeated 15 times to reach an overall thickness of 9 microns forthe dielectric film stack 142. In other embodiments in which the overallthickness of the dielectric film stack is 9 microns, a repeating stackof 45 constituent layers of 100 nm each can be implemented in which theoverall repeating structure 142 a-142 c need only be repeated twice toachieve the overall thickness. In yet other embodiments, the repeatingstructure 142 a-142 c of dielectric stack 142 has a layered filmstructure that does not repeat because the total number of constituentfilms in the repeating stack provides sufficient overall film thicknessfor the film structure 142 (FIG. 1B).

In preferred embodiments, the repeating film structure 142 is acomposite structure of repeating stacks. In embodiments with therepeating stack 142 a, the overall thickness of repeating film structure142 is the combined thickness of the repeating stack 142 a, 142 bmultiplied by the number of times that the repeating stack 142 a-142 bis repeated. For example, the repeating film structure 142 a for apreferred embodiment in which the first layer 143 is 900 nm and thesecond layer 144 is 50 nm has a total repeating stack thickness of 950nm and when repeated 9 times, the resulting combined film thickness fordielectric stack 142 is 8590 nm ((900 nm+50 nm)×9=8590 nm)). Similarly,in another preferred embodiment, the repeating film structure 142 a,which has a first layer 143 that is 40 nm with a refractive index of1.7, and which has a second layer 144 that is 500 nm in thickness with arefractive index of 1.65, has a combined thickness for repeating stack142 of 540 nm, and when repeated 10 times, has a resulting combined filmthickness for dielectric stack 142 of 5400 nm ((500 nm+40 nm)×10=5400nm)) (FIG. 1B).

Generally, the overall dielectric stack 142 is made sufficiently thickto provide the low optical loss for optical signals transmitted throughthe resulting waveguide structure 140. The multilayer structure,deposited at low temperatures, ensures low stress in the resulting filmstructure and enables thick waveguides (2000 nm to 25000 nm) to beformed. Waveguide structures 140 are thus sufficiently thick to enabletransmission of the optical signals with little interaction of thetransmitted optical signals with the substrate, interaction levels thatcould lead to undesired attenuation of the transmitted signals.

It is to be understood that the thickness, the number of films, and therefractive index for the films in dielectric stack 140 can vary andremain within the scope of the current invention. The refractive indexof silicon oxynitride films can vary in the range of 1.4 to 2.02. As theconcentration of nitrogen in deposited silicon oxynitride films isminimized, the refractive index approaches the index of refraction ofsilicon dioxide, 1.445. Conversely, as the concentration of oxygen isminimized in the deposited films, the refractive index approaches theindex of refraction of silicon nitride, 2.02. The index of refractioncan thusly be varied in the range of 1.445 to 2.02 by varying thestoichiometric concentration of silicon, oxygen, and nitrogen in thedeposited films. In embodiments, the index of refraction for theconstituent films 143, 144 in the repeating dielectric film stack 142 a,for example, are varied in the range of 1.445 to 2.02 to produce thickfilm structures of 2000 to 25000 nm, or greater, and that provide lowstress and low optical signal losses, in dielectric film stacks 140.

In another preferred embodiment, the dielectric film stack 142 includesa repeating stack 142 a with a first layer 143 of silicon oxynitridewith thickness of 60 nm and an index of refraction of 1.7 and a secondlayer 144 of silicon oxynitride with thickness of 500 nm and an index ofrefraction of 1.65. Repeating dielectric stack structure 142 a isrepeated in an embodiment 13 times for a total thickness for dielectricfilm stack 142 of 7280 nm. It is to be understood that the total numberof repeating film stacks 142 a can vary. In some preferred embodiments,the number of repeating film stacks 142 a is three to twenty. In someother preferred embodiments, the repeating film stack 142 a is such toproduce a total dielectric film structure 142 that in some embodimentsis greater than 2000 nm in thickness and in some embodiments less than25000 nm. In yet other preferred embodiments, the total dielectric filmstructure 142 is in the range of 8000 to 12000 nm. In yet otherembodiments, the number of repeating film stacks 141 is two or more andthe thickness of the dielectric film structure 142 is greater than 2000nm and less than 25000 nm (FIG. 1B).

In some embodiments, the thickness for the first film 143 is in therange of 5 nm to 1000 nm. In some other embodiments, the thickness ofthe second film 144 is in the range of 5 nm to 1000 nm. In these andother embodiments, the thickness of the dielectric film structure 142,which is the sum of the thicknesses of the repeating film structures 142a, is greater than 2000 nm in thickness. In preferred embodiments, thethickness of the sum of the repeating film structures 142 a is in therange of 4000 to 10000 nm.

It is to be understood that the repeating film structure 142 a is anintegral component of the inventive dielectric stack structure 140. Itis also to be understood that the number of films, the film thicknesses,the refractive indices, and the resulting composition of the films canbe varied and remain within the spirit and scope of the inventivedielectric stack structure 140, and in the practice of utilizing thedielectric stack structure 140 to provide low stress and low opticalloss for signals transmitted through waveguides that are fabricated fromthe dielectric stack structure 140. In this regard, in some embodiments,an initial repeating film structure 142 a is used for two or more of thefilms in the dielectric stack 142, and then a different repeating filmstructure 142 a is used for another two or more films in the samedielectric film structure 140 to produce inventive dielectric stack 140.It is to be further understood that an initial repeating film structure142 a can be used for two or more of the films in the dielectric filmstructure 142, a different repeating film structure 142 a, can be usedfor another two or more films in the same dielectric film structure 142,and then any number of additional repeating film structures 142 a withthe same or different repeating film structures can be used for two ormore additional films in the dielectric film structure 140 and remainwithin the scope and spirit of the embodiments. In the foregoingdiscussion, the variations in the first film 143 and second film 144 canbe produced with one or more variations in the refractive index, thethickness, and the composition or stoichiometry of the films (FIG. 1B).

It is also to be understood that in some embodiments, first film 143 inthe repeating film structure 142 a can include one or more films andremain within the scope of the invention. In an embodiment, first film143 in repeating film structure 142 a, for example, is 500 nm inthickness with a refractive index of 1.7. In another embodiment, firstfilm 143 includes a first part that is 250 nm in thickness with arefractive index of 1.7 and a second part that is 250 nm in thicknesswith a refractive index of 1.65. In yet another embodiment, the firstfilm 143 in the repeating film structure 142 a has a refractive index of1.68 with a first partial thickness that is 250 nm and a second partialthickness that is deposited in a separate process step from the first,for example, and that is also 250 nm in thickness for a combinedthickness of 500 nm for the two partial films of the first film 143 ofrepeating film structure 142 a (FIG. 1B).

In some embodiments, the first film 143 has a graded refractive index orstoichiometric composition. Gradations in the composition of the firstfilm 143 of the repeating film structure 142 a, for example, remainwithin the scope of the current invention. In some embodiments, therefractive index varies through part or all of the thickness of thefirst film 143. Similarly, in some embodiments, the stoichiometriccomposition varies through part or all of the thickness of the firstfilm 143. Variations in the refractive index or the stoichiometriccomposition of the first film 143 within the thickness of this filmremain within the scope of the current invention (FIG. 1B).

It is also to be understood that in some embodiments, second film 144 inthe repeating film structure 142 a can include one or more films andremain within the scope of the invention. In an embodiment, second film144 in repeating film structure 142 a, for example, is 500 nm inthickness with a refractive index of 1.7. In another embodiment, secondfilm 144 includes a first part that is 250 nm in thickness with arefractive index of 1.7 and a second part that is 250 nm in thicknesswith a refractive index of 1.65. In yet another embodiment, the secondfilm 144 in the repeating film structure 142 a has a refractive index of1.68 with a first partial thickness that is 250 nm and a second partialthickness that is deposited in a separate process step from the first,for example, that is also 250 nm for a combined thickness of 500 nm forthe two partial films of the second film 144 of the repeating filmstructure 142 a (FIG. 1B).

In some embodiments, the second film 144 has a graded refractive indexor stoichiometric composition. Gradations in the composition of thesecond film 144 of the repeating film structure 142 a, for example,remain within the scope of the current invention. In some embodiments,the refractive index varies through part or all of the thickness of thesecond film 144. Similarly, the stoichiometric composition variesthrough part or all of the thickness of the second film 144. Variationsin the refractive index or the stoichiometric composition of the secondfilm 144 within the thickness of this film remain within the scope ofthe current invention (FIG. 1B).

In some embodiments, repeating structure 142 has an unequal number offirst layers 143 and second layers 144. In some embodiments, repeatingstructure 142 includes a first layer 143 positioned between two secondlayers 144 (FIG. 1B).

In preferred embodiments, top spacer layer 150 is one or more layers ofsilicon dioxide or silicon oxynitride. In some embodiments, singlespacer layer 150 a is a layer of one type of material, such as silicondioxide. In some preferred embodiments, single spacer layer 150 a is alayer of silicon oxynitride. In yet other preferred embodiments, thesingle spacer layer 150 a is a layer of silicon oxynitride withrefractive index of 1.55 and with a thickness of 500 nm. In yet otherembodiments, single spacer layer 150 a is a layer of silicon oxynitridewith thickness in the range of 0 to 1000 nm. Although in preferredembodiments, a spacer layer 150 a is included in the structure, in someother embodiments, the spacer layer 150 can be combined with an optionaltop layer, can be made very thin, or is not included (FIG. 1A).

Spacer layer 150 can be a composite spacer layer 150 b of one or morelayers of silicon oxynitride or silicon dioxide. In an embodiment,composite spacer layer 150 b includes two layers of silicon oxynitridewith thicknesses of 250 nm and with a composite refractive index ofapproximately 1.55. In some embodiments, the sum of the thicknesses ofthe two layers in composite spacer layer 150 b is in the range of 1 to1000 nm (FIG. 1A).

Similarly, the spacer layer 150 can be a composite layer 150 c of threeor more layers with the same or different thicknesses and refractiveindices, that when combined, provide a total thickness in the range of 1nm to 1000 nm and a composite refractive index in the range of 1.4 to2.02 (FIG. 1A).

Optional top layer 158 is one or more layers of a dielectric materialsuch as silicon dioxide, silicon nitride, aluminum oxide, and aluminumnitride, among others. In some embodiments, a top layer 158 of silicondioxide with thickness of 200 nm and a refractive index of 1.445 isused. In some embodiments, the film thickness of the top layer is in therange of 0 to 500 nm. In some embodiments, silicon oxynitride is used inthe optional top layer 158. In some embodiments, another dielectricmaterial or combination of materials such as aluminum nitride oraluminum oxide is used. In some embodiments, no optional top layer 158is provided.

The advantages of the current invention with regard to achievable rangesof the measured film stress for films that can be implements infabricating dielectric film structures are shown in FIG. 2 for someembodiments. In FIG. 2A, the measured film stress is shown for a rangeof thicknesses for the inventive dielectric film stacks. FIG. 2A showsthat the film stress can be controlled to less than approximately 20 MPafor embodiments as thick as approximately 18 um. These relatively lowstress levels are not achievable or very difficult to achieve in filmsof a single thick layer of material such as silicon dioxide or siliconoxynitride. In FIG. 2B, the measured stress levels for deposited siliconoxynitride films are shown for films of various refractive indices. Asshown, the refractive index is a convenient means for assessingvariations in film properties for deposited films. The capability toachieve control of the stress in the individual films over a wide range,allows for the fabrication of very thick dielectric film structures(1000-25000 nm, and greater) with optical properties that are suitablefor use as planar waveguides. In embodiments, stress levels arecontrolled in planar waveguide structures to minimize deformation of thesubstrates upon which the thick dielectric stacks are deposited, and toachieve low optical signal loss in waveguides fabricated from thesethick dielectric film structures.

Referring to FIG. 3, the measured optical losses from some embodimentsof the inventive dielectric stack structures are shown. Optical signallosses for practical use in planar waveguide structures of less thanapproximately 1 dB/cm are desirable. FIG. 3A shows that these levels areachievable for a range of measured composite refractive indices from theinventive dielectric stack structures. In addition to the properties ofthe dielectric stack structure itself, the buffer layer also has aninfluence on the measured losses for optical signals transmitted throughwaveguides fabricated from the inventive dielectric stack structures.FIG. 3B shows how the thickness of the buffer layer in some embodimentsaffects the measured optical losses. As the thickness of the bufferlayer is increased in these embodiments, the resulting optical lossesare reduced to values of much less than 1 dB/cm.

Referring to FIG. 4, steps in the formation of embodiments of thedielectric films and film structures are provided. In FIG. 4A, formingstep 400 in the process of forming embodiments of the inventivedielectric stack 140 of silicon oxynitride films at low temperaturehaving low stress and low optical loss is shown. Low temperature in FIG.4A refers to the temperature of the deposition of the films used in thefabrication of the dielectric stacks, namely less than 500° C. in someembodiments, and in other embodiments, less than or equal to 300° C. Lowstress in FIG. 4A refers to stress levels in the deposited films in filmstructure 140 of less than or equal to approximately 20 MPa, eithercompressive or tensile. Low optical loss in FIG. 4A refers to opticallosses in embodiments of deposited dielectric film stacks 140 of lessthan approximately 1 dB/cm. The forming step 400 provides for theformation of thick structures of dielectric silicon oxynitride filmswith low stress, and suitable for use in the transmission of opticalsignals with low loss.

Referring to FIG. 4B, the forming steps 420 in embodiments for whicheach individual layer in the inventive dielectric stack 140 of siliconoxynitride films is deposited at low temperature, and with low stressand low optical loss is shown. Low temperature in FIG. 4B refers to thetemperature of the deposition of the films used in the fabrication ofthe dielectric stacks, namely less than 500° C. in some embodiments, andin other embodiments, less than or equal to 300° C. Low stress in FIG.4B refers to stress levels in the deposited films of less than or equalto approximately 20 MPa, either compressive or tensile. Stress levels ofless than 20 MPa in deposited films ensure minimal substrate deformationand reduce the likelihood that the films will delaminate. Low opticalloss in FIG. 4B refers to optical losses in embodiments of depositeddielectric film stacks 140 of less than approximately 1 dB/cm. Formingstep 420 provides for the formation of thin composite films ofdielectric silicon oxynitride deposited sequentially at low temperaturesof less than 500° C. to form the thick dielectric stack structures 140with low stress, and suitable for use in the transmission of opticalsignals with low loss.

Referring to FIG. 4C, steps in the formation of planar waveguides from aforming step 440 and a patterning step 450 are shown for someembodiments. Formation of the individual dielectric films and thedielectric film structures 440 for the inventive stack structure 140 areshown that include the formation of a dielectric stack of siliconoxynitride films on a substrate 110 with a stack structure that includesa buffer layer 130, one or more optional bottom spacer layers 138, arepeating stack of one or more dielectric layers 142, one or moreoptional top spacer layers 150, and an optional top layer 158.Embodiments for the forming of the dielectric film and film structures440 utilize one or more of forming step 400 and forming step 420.Patterning step 450 is combined in embodiments with forming step 440 onthe resulting dielectric stack to form one or more planar waveguidesfrom the dielectric stack structures 140. Patterning steps can includethe use of established photoresist patterning processes, in whichphotosensitive layers are used either directly as a means fortransferring a pattern with subsequent dry or wet etch processing, orvia a hard mask in which the photoresist is first used to transfer apattern to a hard mask layer that is then used to transfer the waveguidepattern from the hard mask layer to the dielectric stack layer.Processes for photoresist patterning and subsequent wet and dry etchingof film structures are well established for those skilled in the art ofdielectric film patterning techniques.

Typical deposition processes for dielectric films used in semiconductordevice manufacturing include chemical vapor deposition (CVD), plasmaenhanced chemical vapor deposition (PECVD), metalorganic chemical vapordeposition (MOCVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), among others.

In embodiments, deposition of the inventive dielectric film structure140 is accomplished using PECVD. In other embodiments, deposition of theinventive dielectric film structure 140 is accomplished using one ormore of the thin film deposition techniques that include chemical vapordeposition (CVD), plasma enhanced chemical vapor deposition (PECVD),metalorganic chemical vapor deposition (MOCVD), physical vapordeposition (PVD), and atomic layer deposition (ALD).

Process parameters such as the process pressure, substrate temperature,and process power levels, as well as the selection of precursor gasesand the flows of these and other gases used in the process, amongothers, can each affect the resulting properties of the deposited films.In the fabrication of nitrogen-containing films such as silicon nitrideand silicon oxynitride, for example, precursors such as ammonia gas(NH₃), a source of nitrogen, and silane (SiH₄), a source of silicon, arecombined in a plasma environment to facilitate the formation of the thinsilicon nitride films. The ammonia and silane can be further combinedwith one or more oxidizing gases such as oxygen (O₂), nitric oxide (NO),and nitrous oxide (N₂O) to incorporate oxygen into the growing films toform silicon oxynitride. The properties of the silicon nitride and thesilicon oxynitride films can be affected by the specific selection ofgases in the process mixture and the ratio of the specific gas flows inthe mixture. Residual impurities, such as hydrogen, can also affect theproperties of the deposited films, particularly through the formation ofnitrogen-hydrogen bonds in the deposited films. In embodiments, aprocess is provided to fabricate dielectric film structure 140 in whichone or more nitrogen precursors that do not contain hydrogen are used inthe formation of thin films of silicon nitride and silicon oxynitride toreduce the residual hydrogen concentration in the deposited films.

In embodiments, plasma enhanced chemical vapor deposition (PECVD), asshown for example in the schematic drawing in FIG. 5, is used to depositsilicon oxynitride film structures 140. PECVD processes are mosttypically performed under vacuum conditions with precursor gasesspecific to the types of films that are targeted for deposition.Substrates are most typically heated to elevated temperatures. In theconfiguration shown in FIG. 5, radio frequency (rf) power iscapacitively coupled to the electrode opposite to that on which thesubstrate resides during the process. In the PECVD system depicted inFIG. 5, substrates reside on the lower electrode during processing, andthe rf power is applied to the upper electrode. In embodiments in whichthe power is applied to the upper electrode, the substrate is notsubjected directly to high energy ion bombardment as would beanticipated if the substrate were to be placed on the rf poweredelectrode.

In an embodiment of the present invention, multilayer dielectric filmstructure 140 is formed using PECVD technology with a process chemistrythat utilizes hydrogen-free nitrogen and oxygen precursors to yieldplanar waveguides with low optical loss and low stress. PECVD technologyis widely used in semiconductor and optical device fabrication. Much ofthe equipment used in the manufacturing of semiconductor devices can beused in the fabrication of optical devices and the use of the term“semiconductor device fabrication” herein is intended to include opticaldevice fabrication. The fabrication of the optical devices and opticalsubassemblies, utilize, or have the potential to utilize, the techniquesand practices used in semiconductor device fabrication.

In embodiments, the dielectric film stack 140 is deposited onto asubstrate using PECVD technology at temperatures in the range of200-500° C. In other embodiments, the substrate temperature duringdeposition of the dielectric film structure 140 is in the range ofapproximately 250-400° C. In yet other embodiments, the dielectric filmstack 140 is deposited onto a substrate using PECVD technology attemperatures of approximately 300° C. And in yet another embodiment, thedielectric film stack 140 is deposited at or approximately 300° C. usinga gas mixture of silane, nitrogen, and nitrous oxide. In yet anotherembodiment, the dielectric film stack is deposited using a gas mixtureof silane, nitrogen, and oxygen. In yet another embodiment, thedielectric film stack 140 is deposited at or approximately 300° C. usinga gas mixture of silane, nitrogen, and nitric oxide.

In general, a gas mixture used in the deposition of silicon oxynitridefilms must contain at least the primary stoichiometric constituents orelements of the film, namely, silicon, oxygen, and nitrogen. Control ofthe deposited dielectric film properties is achieved, in part, with thecontrol of the gas flows and mixture ratios of the constituent precursorgases in the deposition system. In an embodiment, for example, silanegas (SiH₄) is used as a precursor to provide the silicon, nitrogen gas(N₂) is used as a precursor for nitrogen, and oxygen gas (O₂) is used asa precursor for oxygen. In embodiments, the independent control of oneor more of the gas flows, the ratios of the gases, and the partialpressures of these three gases in the deposition system can provide ameans for independent control of the ratio of the three elements, namelySi, N, and O, in the deposited films.

In embodiments, silane gas, one of the most commonly used precursors forthe deposition of silicon and silicon-containing thin films in epitaxialand chemical vapor deposition processes in semiconductor devicefabrication, is provided as a source for silicon in the deposited filmstructure 140. In other embodiments, one or more of a silicon precursorthat includes dichlorosilane, trichlorosilane, methylsilane, silicontetrachloride, chlorosilane, dichlorosilane, and trichlorosilane isutilized as a silicon precursor in the deposited dielectric filmstructure 140.

In embodiments, a silicon-containing precursor gas that may or may notcontain hydrogen, is combined with a hydrogen-free precursor gas fornitrogen, and a hydrogen-free precursor gas for oxygen to produce theoxynitride layers in the dielectric stack structure 140. In otherembodiments, silane (SiH₄) is used as the silicon precursor in the PECVDdeposition of silicon oxynitride films. In yet other embodiments, silaneis used as the silicon precursor and is mixed with hydrogen-freeprecursors for nitrogen and oxygen to form films of silicon oxynitride.

In addition to the source of silicon in one or more of the precursors inthe deposition gas mixture, precursors for embodiments with siliconoxynitride in the dielectric film structure 140 include one or more ofan oxygen-containing precursor, a nitrogen-containing precursor, and aprecursor that contains both oxygen and nitrogen. Precursors thatcontain both oxygen and nitrogen elements in embodiments include nitrousoxide, nitric oxide, nitrogen dioxide, dinitrogen tetraoxide, andmixtures of these gases, for example. In other embodiments, anitrogen-containing precursor that does not contain oxygen is used incombination with an oxygen-containing precursor that does not containnitrogen. In an embodiment, nitrogen gas (N₂) is the nitrogen-containingprecursor and is combined with oxygen gas (O₂) as the oxygen-containingprecursor, and further combined with silane or anothersilicon-containing precursor described herein in a plasma enhancedchemical vapor deposition system. In yet other embodiments, anitrogen-containing precursor such as nitrogen gas is combined with oneor more precursors that contain both oxygen and nitrogen, such asnitrous oxide and nitric oxide, or a mixture thereof, and furthercombined with silane or another silicon-containing precursor asdescribed herein in a plasma enhanced chemical vapor deposition systemto form the silicon oxynitride layers in dielectric stack 140. In yetother embodiments, an oxygen-containing precursor such as oxygen gas iscombined with one or more precursors that contain both oxygen andnitrogen, such as nitrous oxide and nitric oxide, and further combinedwith silane or another silicon-containing precursor in a plasma enhancedchemical vapor deposition system or other deposition system as describedherein to form dielectric stack 140. Oxygen-containing precursorsinclude atomic oxygen, molecular oxygen, ozone, carbon monoxide, andcarbon dioxide.

And in yet other embodiments, one or more of argon, helium, neon, xenon,nitrogen, and oxygen is added to the gas mixtures described herein inembodiments as a diluent. Diluents are often utilized in semiconductordeposition processes to slow the deposition rate, to enhance theignition of the plasma in plasma-based processes, to improve depositionuniformity, and to alter or modify the energy absorption profile of thegaseous species in the plasma, among other potential benefits. Additionof one or more diluents listed herein to the processes described hereinremains within the scope of the current invention.

In embodiments, the use of hydrogen-free, nitrogen and oxygen precursorsin the deposition of the inventive dielectric film stacks yields lowstress silicon oxynitride film structures from which waveguides can beformed that exhibit low optical signal loss.

In other embodiments, low stress, low optical loss silicon oxynitridefilm structures are formed using plasma enhanced chemical vapordeposition with a gas mixture that contains one or more of each of asilicon-containing precursor, a nitrogen-containing precursor, and anoxygen-containing precursor.

Referring to FIG. 6, a plot of the refractive index is shown for siliconoxynitride films deposited using such a gas mixture in a PECVD system.The ordinate in the plot in FIG. 6 shows the flow rate of a molecularprecursor gas that contains silicon and the abscissa shows therefractive indices for a measurement wavelength of 633 nm thatcorrespond to specific values of the precursor gas flow rate used in thedeposition of the inventive dielectric stack structures 140. The plotincludes sample data that show the variation in a representative opticalproperty, namely the refractive index, for silicon oxynitride films thatwere deposited over a range of gas flows for the silicon-containingprecursor, holding other gas flows and PECVD system parameters constant.

The data provided in FIG. 6, when combined with the measured stressesover a similar range of refractive indices as provided in FIG. 2B,demonstrate the benefits of the inventive process as a means to providecontrol of the optical properties (refractive index) and mechanicalproperties (stress) of the deposited films with variation of the gasflow mixture. The range of gas mixtures shown in the exemplary sampledata shown in FIG. 6, produced with variations in the silicon-containingprecursor gas flow, provide a wide range of measured refractive indicesfor silicon oxynitride films. The variation in the measured refractiveindex are shown in FIG. 2B to produce the low values of residual stressin deposited silicon oxynitride films, and that a crossover point ofzero stress can be produced a specific value of the silicon-containingprecursor gas flow. The innovation provided using the inventiveprocesses should become increasingly apparent in embodiments in whichthe achievable optical and mechanical properties are further combinedwith the inventive superlattice stack structures described herein forthe dielectric stack structures 140 as described in FIG. 1. Combinationsof refractive index and film thickness yield stack structures inembodiments that have low stress and low optical loss when depositedwith processes that do not contain hydrogen in the nitrogen and oxygenprecursors.

In embodiments of the inventive PECVD processes, a dielectric stackstructure 140 is provided on substrate 100 wherein the ratios of theprecursor gases in the PECVD process are configured to achieve a stresslevel of less than approximately 20 MPa in magnitude. In otherembodiments, the dielectric stack structure 140 is a structure ofsilicon oxynitride layers deposited in a PECVD system using a processthat contains silane, nitrogen, and nitrous oxide wherein the ratios ofthese precursor gases are configured to achieve a stress level that isless than or approximately 20 MPa. In embodiments, control of the stressis achieved with the ratios of the gases in combination with the filmthicknesses of the individual layers in the dielectric film structure140, as described in examples provided herein.

In embodiments of the dielectric stack structures 140, for example, thestoichiometric concentrations of the individual layers are selected, asreflected in the measured refractive index of the individual layers inthe stack structure, and optimized along with the layer thicknesses toproduce low stress film structures with low optical signal losscharacteristics. In the formation of the stacked dielectric structure140, the total composite refractive index and the stress level in thefilm stack 140 are affected by the number of layers, the characteristicsof the interfaces between the layers, the stoichiometric concentration,the resulting density of the deposited films, and the presence ofimpurities in the deposited films. This suggests that the measuredrefractive index may not be unique. Although the refractive indexprovides an effective method for characterizing the effect of changes inprocess parameters such as the gas flow on the optical properties of thedeposited dielectric films, multiple stoichiometric concentrations mayexist for the elemental constituents of the silicon oxynitride layer fora given value of refractive index. Nonetheless, the refractive index isan effective means for providing a measure of changes in the filmproperties, and most notably, a measure of the residual stress in thedeposited films.

The data shown in FIG. 6 is provided for demonstrative purposes in thatthe process parameters such as plasma power, gas pressure, substratetemperature, and gas ratios in the PECVD system can influence themeasured refractive index. The effects of the variation in therefractive index are likely a reflection of the variation in thestoichiometric concentrations and perhaps the density of the depositedfilms. It is important to note, therefore, that the refractive index maynot be unique to a single stoichiometric combination of silicon, oxygen,and nitrogen in the silicon oxynitride layers.

Variations in the embodiments in which the inventive dielectric stackstructure 140 is combined with the silicon, oxygen, and nitrogenprecursors as described herein remain within the scope of the currentinvention.

In embodiments, the low stress, low optical loss dielectric filmstructures 140 are formed using plasma enhanced chemical vapordeposition with a gas mixture that does not include hydrogen-containingprecursors for either nitrogen, oxygen, or both, or that includesconcentrations of these gases that are low enough so as to not requirehigh temperature processing of greater than 500° C. for example, or highthermal budget processes, to achieve the low optical signal losses ofless than 1 dB/cm in waveguides fabricated from the inventive dielectricstack structure 140. In some embodiments, a small amount ofhydrogen-containing nitrogen or oxygen precursor gas, or both, ofapproximately 5-10% or less of the total precursor gas flow, is added tothe PECVD gas mixture. In these embodiments, the concentrations ofhydrogen-containing nitrogen and oxygen precursors are low enough so asto not require high thermal budget processes to achieve the low opticalsignal losses of less than 1 dB/cm in waveguides fabricated from theinventive dielectric stack structure 140. In yet other embodiments, anitrogen-containing precursor such as nitrogen gas is combined with asmall amount of a hydrogen-containing precursor gas, such as ammonia,for example, and one or more precursors that contain both oxygen andnitrogen, such as nitrous oxide and nitric oxide, and further combinedwith silane or another silicon-containing precursor as described hereinin a plasma enhanced chemical vapor deposition system to form thesilicon oxynitride layers in the dielectric stack 140. In theseembodiments, the amount of ammonia in the process should be sufficientlylow, less than approximately 10% of the total gas flow for example, soas to not require high temperature processing of greater than 500° C.for example, or processing with high thermal budget processes, toachieve the low optical signal losses of less than 1 dB/cm in waveguidesfabricated from the inventive dielectric stack structure 140. Althoughincreases in the optical signal loss are to be expected, the inclusionof small amounts of ammonia to the gas mixture will increase thedeposition rate of the silicon oxynitride films.

FIG. 2B shows the variation in the measured stress levels in depositedsilicon oxynitride films over a range of measured refractive index forthese films. The data in FIG. 2B show that the stress in the depositedfilms using the inventive process can be varied over a wide rangebetween compressive stress and tensile stress with the crossover at 0MPa in the measured stress observed at the transition between the filmsbeing in tension and compression. In embodiments, the stress in eachlayer in the inventive stack structures is varied such that the totalstress in the dielectric film structure as shown in FIG. 1 is less thanapproximately 20 MPa. The stresses in each of the layers of theinventive stack structure as described in FIG. 1, is controlled inembodiments by varying the gas ratio, as for example as shown in FIG.2B, and by varying the corresponding thickness of the layers. Examplesof combinations of specific refractive indices, produced with variationsin the nitrogen to nitrous oxide gas ratio, are described herein.

In embodiments, when the use of hydrogen-free nitrogen and oxygenprecursors is combined in the deposition chemistry with substratetemperatures during deposition of less than 400° C. in embodiments, andof approximately 300° C. in yet other embodiments, the resulting filmstacks can be produced that exhibit stress levels of less than 20 MPa.Additionally, in embodiments, the inventive film stacks are patterned toform optical waveguides that provide low losses for optical signalstraveling within these waveguides. Examples of embodiments of thedeposited dielectric film stacks are described herein, and in particularare described in the relevant discussion of FIG. 1 described herein.

In embodiments, the stack of silicon oxynitride films is formed onto asubstrate using a PECVD process for which the process parameters,including the precursor gas ratios, are configured to achieve a stresslevel of less than 25 MPa, and in preferred embodiments less than 20MPa. Measured stress levels in the deposited film stacks of less than 20MPa greatly reduce the potential for either the substrate to deform, thedeposited films to delaminate, or for some other undesired effect tomanifest in either the waveguide or the finished subassembly thatincludes the waveguide. Substrate deformation and film delamination arejust two forms of damage that can occur when stresses in the depositedfilm structures are not properly controlled. In embodiments, thedeposited dielectric film stacks with stress levels of less than 20 MPaare patterned into one or more of waveguides and optical devices.

In yet other embodiments, a stack of silicon oxynitride films are formedonto a substrate using a PECVD process for which the gas ratios areconfigured to achieve a stress level of less than 20 MPa and for whichthe process chemistry includes a silicon-containing precursor that mayor may not contain hydrogen, and one or more molecular precursors thatcontain nitrogen or oxygen elements that contains little or no ammoniaor other hydrogen-containing gas. In embodiments, the deposited filmstacks with stress levels of less than 20 MPa that are deposited usingnon-hydrogen-containing nitrogen and oxygen gas sources are patternedinto one or more of waveguides and optical devices.

In yet other embodiments, a stack of silicon oxynitride films are formedonto a substrate using a PECVD process for which the gas ratios areconfigured to achieve a stress level of less than 20 MPa and for whichthe process chemistry does not include ammonia or otherhydrogen-containing gas, other than silane. Silane (SiH₄) is widely usedin industry for the deposition of silicon-containing films and is usedin some embodiments. In embodiments, the deposited film stacks withstress levels of less than 20 MPa, that are deposited usingnon-hydrogen-containing nitrogen and oxygen gas sources such asnitrogen, oxygen, nitric oxide, and nitrous oxide, for example, arepatterned into one or more of waveguides and optical devices.

In embodiments, the gas pressure in the PECVD system during thedeposition of the silicon oxynitride films can be in the range of 1 mTto 100 Torr to produce dielectric film stack structures. In otherembodiments, process pressures are in the range of 50 mTorr to 2 Torr.In yet other embodiments, process pressures are in the range of 100 to5000 mTorr. The process pressure need not be the same for every step inthe deposition sequence required to produce the full dielectric filmstructure 140.

In embodiments, the total gas flows during deposition of inventivedielectric stack structure 140 used in the inventive dielectricinterposers can vary in the range of 5 sccm to 5000 sccm. In someembodiments, the silane gas flow is in the range of 5-1000 sccm. Inother embodiments, the silane gas flow, or other silicon-containingprecursor gas, is in the range of approximately 10-100 sccm.

In embodiments, the nitrogen and oxygen precursor gas flows can varyover a wide range. In some embodiments, the nitrogen and oxygenprecursor gas flows are in the range of 0 to 5000 sccm.

In some embodiments, for which nitrogen is combined with nitrous oxideor nitric oxide, the nitrogen gas flow and nitrous oxide gas flows arein the range of 0 to 5000 sccm. And in some other embodiments, for whichoxygen is combined with nitrous oxide or nitric oxide, the oxygen gasflow and nitrous oxide gas flows are in the range of 0 to 5000 sccm.

In a PECVD system, the input power to the plasma can vary over a widerange. Typical input power for the dielectric stacks in embodiments isapproximately 25-2000 W. In some embodiments, the input power duringplasma enhanced deposition steps is in the range of 200 to 700 W. In yetother embodiments, the input power during plasma enhanced depositionsteps is in the range of 500 to 1200 W. The process power need not bekept constant for the deposition of each of the films in the dielectricstack structure 140 but can vary from step to step, or within adeposition step.

In embodiments, one or more frequencies in the range of 1 kHz to 1 GHzcan be used for the rf power provided to the plasma. In an embodiment, afrequency of 13.56 MHz is used to generate the plasma. In otherembodiments, other frequencies or combinations of frequencies are usedto generate the plasma. In some other embodiments, rf power with afrequency of approximately 27 MHz is applied to the powered electrode.In a preferred embodiment, 13.56 MHz rf power is applied to the upperelectrode with the substrate residing on a grounded electrode during thedeposition of the dielectric film structure 140. In other embodiments,the electrode upon which the substrate resides during the depositionprocess is not grounded. In yet other embodiments, the power is appliedto both the upper and lower electrodes, divided either equally orunequally.

Power can be delivered to the PECVD system in either capacitive orinductive operational modes and remain within the scope of the currentinvention. For inductive-coupled PECVD systems, the plasma is typicallygenerated with power that is delivered to the plasma via an antenna andthe wafer typically resides on a bottom electrode similar to that shownin the capacitively coupled configuration shown in FIG. 5.

Inert gases, such as argon and helium, can be added to the gas mixture,to yield dielectric film stacks with similar properties and remainwithin the scope of the current invention. Inert gases are frequentlyadded to deposition process chemistries to modify film properties, suchas the stoichiometry or density of the film. In embodiments, argon isadded to a gas mixture of silane, nitrous oxide, and nitrogen. In yetother embodiments, helium is added to the gas mixture of silane, nitrousoxide, and nitrogen. In yet other embodiments, one or more of argon andhelium is added to a process gas mixture that includes asilicon-containing precursor gas that may or may not contain hydrogen, anitrogen precursor that does not include hydrogen in thenitrogen-containing precursor gas molecule or molecules, and an oxygenprecursor gas that does not contain hydrogen in the oxygen-containingprecursor gas molecule or molecules. Examples of nitrogen precursorsthat do not include hydrogen include molecular nitrogen (N₂), nitrousoxide (N₂O), and nitric oxide (NO). Examples of oxygen precursors thatdo not include hydrogen include molecular oxygen (O₂), nitrous oxide(N₂O), nitric oxide (NO), carbon monoxide (CO), and carbon dioxide(CO₂).

Commercially available deposition systems such as the APM PECVD modelmanufactured by SPTS provide advanced programmability for the depositionof the overall dielectric film structure 140 and for each step in thedeposition process. The programmability of commercially availabledeposition systems enables automated operation of the system hardwarethat includes, for example, the mass flow controllers, the source powersupply or supplies, the temperature controllers, and the pressurecontrollers. The process parameters such as, for example, the gas flowrates, the power level or levels, the pressure, the substratetemperature, among other parameters for each step in the deposition of afilm structure can be programmed into a process recipe. Use ofprogrammable and commercially available deposition systems is widelyused in the industry and the use of programmable deposition systems isanticipated and with the scope of the current invention.

Referring to FIG. 7A, a cross sectional schematic of an embodiment ofthe inventive optical dielectric interposer structure 500 is shown. Inthis figure, an embodiment for interposer 700 includes substrate 710,optional interconnect layer 720, and planar dielectric stack structure740 disposed on the optional interconnect layer 720. Terminal padopening 725 in the interconnect layer 720 provides for connections ofoptical die to the interconnect metal lines. In some embodiments, thetop intermetal dielectric 727 in the interconnect layer resides belowthe dielectric stack 740 as shown in FIG. 7A. The interconnect layer 720is a structure of metal lines 726 and intermetal dielectric films 727that provide metal traces for mounting optical devices and forinterconnecting electrical and optoelectrical die on the dielectricinterposer 700. In some embodiments, the top layer of the interconnectlayer 720 may be electrically conductive or insulating, or may beelectrically conducting in some areas and insulating in some areas. Inpreferred embodiments in which optical, electrical, or optoelectricaldie are mounted onto the interposer 700, metal traces are routed withinthe interconnect layer 720 that are accessible through openings 725 toprovide electrical and mechanical connections for the optical,electrical, and optoelectrical devices in, on, or connected to theinterposer 700. It is to be understood that the mounting of purelyoptical die (i.e, die that have an optical function but that are notelectrical) as in a discrete waveguide for example, can benefit from themethods of mechanical attachment commonly used in the attachment ofelectrical die. Attachment of purely optical devices using electricalbond pads is within the scope of the current invention as describedherein. It is also important to note that the top layer of theintermetal dielectric 727 can provide the same functionality as thebuffer layer 730 in some embodiments as shown in FIG. 7A.

The inclusion of optical, electrical, and/or optoelectrical devices,forms a submount assembly 705 from the inventive optical dielectricinterposer 700. FIG. 7B shows a cross sectional schematic of anembodiment of a submount assembly 705 with an optical fiber 790positioned to provide an optical pathway for the transmission of opticalsignals between the optical fiber 790 and the planar dielectric stack740. FIG. 7B also shows optical, electrical, or optoelectrical device760 and electrical device 762 mounted to terminal pad openings 725 ininterconnect layer 720. In an embodiment, optical signals are receivedfrom optical fiber 790 into a waveguide fabricated from the planardielectric stack 740 and routed to device 760 for processing,re-routing, or conversion to electrical signals, for example.

In other embodiments, the optical signals originate on the submountassembly 705 and are transmitted through waveguides fabricated fromplanar dielectric stack structure 740 to the optical fiber 790. In yetother embodiments, the signals are both received from, and transmittedto, the optical fiber 790.

Referring to FIG. 8, cross sectional schematics of embodiments of theinventive optical dielectric interposer structure 800 and the submountassembly 805 are shown. In FIG. 8A, an embodiment for interposer 800includes substrate 810, optional interconnect layer 820, and planardielectric stack structure 840 disposed on the optional interconnectlayer 820. Interconnect layer 820 is typically provided in embodimentsfor which interconnects are required for optical or electrical diemounted on the interposer 800 to form a submount assembly. Terminal padopening 825 in the interconnect layer 820 provides connections for theoptical and electrical die to the interconnect metal lines 826.Interconnect metal lines 826 within interconnect layer 820 forminterconnects between electrical devices mounted onto the interposer800, and in some embodiments, to form electrical connections for devicesexternal to the interposer 800. In embodiments, the planar dielectricstack 840 includes buffer layer 830. In some other embodiments, openingsin the buffer layer 830 provide access to underlying metal layers 826through the interconnect layer openings 825. It is to be understood thatthe buffer layer 830 can be utilized for multiple purposes on theinterposer 800 that include isolation, insulation, vertical spacing,alignment, and control of optical loss. In some embodiments, thepatterning of the buffer layer 830 is not coincident with the pattern ofthe other layers in waveguides that are fabricated from the inventivedielectric stack structure 840. In yet other embodiments, the bufferlayer can be a part of the intermetal dielectric 827 of the interconnectlayer 820.

In embodiments, the intermetal dielectric 827 in the interconnect layer820 generally provides electrical isolation for the metal interconnects826. The interconnect layer 820 is a structure of metal lines 826 andintermetal dielectric 827 that provide insulated electricalinterconnections for the electrical and optoelectrical die on thedielectric interposer 800, and in some embodiments, allow for theinterconnection of devices mounted external to the interposer 800 butfor which connections are required within the interposer 800. It isunderstood that optical devices that do not require electricalinterconnection can also be attached in some embodiments to interconnectlayers for the purpose of mechanical attachment without a specificrequirement for electrical interconnection.

The inclusion of electrical, optical, and/or optoelectric devices formsa submount assembly 805 from the optical interposer 800 on substrate 810with interconnect layer 820. In FIG. 8B, a cross sectional schematic ofan embodiment of a submount assembly 805 with an optical fiber 890positioned to provide an optical pathway between the optical fiber 890and planar dielectric stack 840 is shown. FIG. 8B also showsoptoelectrical device 860 and electrical device 862 mounted throughbuffer layer 830 to terminal pad openings 825 and connected to metalinterconnect lines 826 in interconnect layer 820. In embodiments,intermetal dielectric 827 provides electrical insulation for the metalinterconnects 826. In an embodiment, optical signals are received fromoptical fiber 890, are directed into planar waveguides fabricated frominventive dielectric stack 840, and routed to aligned optical oroptoelectrical device 860 for processing, re-routing, or conversion toelectrical signals, for example.

Referring to FIG. 9, cross sectional schematics of embodiments of theinventive optical dielectric interposer 900 and submount assembly 905are shown. In FIG. 9A, an embodiment for interposer 900 includessubstrate 910, interconnect layer 920, inventive planar dielectric stackstructure 940 disposed on interconnect layer 920, and integratedelectrical device 964. In some embodiments, integrated electrical device964 in the underlying substrate 910 is a transistor, capacitor,resistor, inductor, or other electrical device. In other embodiments,integrated electrical device 964 is a p-channel metal oxidesemiconductor (PMOS) transistor, an n-channel metal oxide semiconductor(NMOS) transistor device or array of one or more of these devices. Insome embodiments, the electrical device 964 is an array of transistordevices based on complementary metal oxide semiconductor (CMOS)technology. In some embodiments, transistor arrays 964 in the substrate910, are used for signal processing, signal conditioning, signalgeneration, memory, and computation, for example. In some embodiments,terminal pad openings 925 in the interconnect layer 920 provideelectrical connections between optoelectrical die and the interconnectmetal lines 926. In some embodiments, the top intermetal dielectric 927in the interconnect layer 920 resides below the dielectric stack 940 asshown in FIG. 9A, and in some embodiments, the upper layer of theintermetal dielectric 927 can also serve as the buffer layer 930. Theinterconnect layer 920 is a structure of metal lines 926 and intermetaldielectric 927 that provide electrical connections for interconnectingelectrical and optoelectrical devices and die that are fabricated on,mounted in, or are connected external to the dielectric interposer 900.

In some embodiments, the top layer of the interconnect layer 920 may beelectrically conductive or insulating. Some parts of the top layer ofinterconnect layer 920 can be insulating, and some parts of the toplayer of interconnect layer 920 can be conductive. In preferredembodiments in which electrical or optoelectrical die are mounted ontothe interposer 900, metal lines 926 are routed within the interconnectlayer 920 to provide electrical connections for the devices in, on, orconnected to the interposer 900, and to underlying electrical devices964.

Submount assembly 905 is formed from the optical dielectric interposer900 by the inclusion of optical, electrical, and optoelectric devices960 onto the interposer 900. FIG. 9B shows a cross sectional schematicof an embodiment of a submount assembly 905 with optical fiber 990positioned to provide an optical pathway between the optical fiber 990and a waveguide fabricated from the inventive planar dielectric stack940. FIG. 9B also shows optoelectrical device 960 mounted to terminalpad openings 925 on interconnect layer 920. In embodiments, opticalsignals are received from optical fiber 990, into planar waveguidesformed from the inventive dielectric stack 940 and routed tooptoelectrical or optical device 960 for processing, re-routing, orconversion to electrical signals, for example. In some embodiments,optoelectrical die 960 are connected to one or more of electricaldevices 964 via metal lines 926 in the interconnect layer 920. In theseembodiments, the optical signals may also originate, wholly or in part,on the submount assembly 905 from which the signals can be transmittedthrough the planar waveguide structures 940 to the optical fiber 990.

In other embodiments, the optical signals originate on the submountassembly 905 and are transmitted through one or more planar waveguidestructures formed from the inventive dielectric stack 940 to the opticalfiber 990. In yet other embodiments, the signals are received from theoptical fiber 990 for one or more of processing, routing, and conversionto electrical signals.

Referring to FIG. 10, cross sectional schematics of embodiments of theinventive optical dielectric interposer 1000 and submount assembly 1005are shown. In FIG. 10A, an embodiment for interposer 1000 includessubstrate 1010, optional interconnect layer 1020, inventive planardielectric stack structure 1040 disposed on the optional interconnectlayer 1020, and integrated electrical device 1064 in substrate 1010

In some embodiments, integrated electrical device 1064 in the underlyingsubstrate 1010 is a transistor, capacitor, resistor, inductor, or otherelectrical device. In other embodiments, integrated electrical device1064 is a p-channel metal oxide semiconductor (PMOS) or n-channel metaloxide semiconductor (NMOS) device, or array of one or more of thesedevices. In other embodiments, electrical device 1064 is an array oftransistors based on complementary metal oxide semiconductor (CMOS)technology. In some embodiments, transistor arrays 1064 in the substrate1010 are used for signal processing, signal conditioning, signalgeneration, memory, and computation, for example. In some embodiments,the terminal pad opening 1025 in the interconnect layer 1020 providesfor electrical connections of optoelectrical die to the interconnectmetal lines 1026 in interconnect layer 1020. In some embodiments, thetop layer of the intermetal dielectric 1026 in the interconnect layer1020 resides below the dielectric stack 1040. In some embodiments, theplanar dielectric stack 1040 includes buffer layer 1030. In yet otherembodiments with buffer layer 1030 in dielectric stack 1040, the bufferlayer 1030 resides within or above the interconnect layer 1020.Interconnect layer 1020 is typically provided in embodiments for whichinterconnects are required for optoelectrical die mounted on theinterposer 1000 to form a submount assembly 1005. The interconnect layer1020 is a structure of metal lines 1026 and intermetal dielectric films1027 that provide metal connections for interconnecting optical,electrical, and optoelectrical devices and dies that are fabricated on,mounted in, or connected external to the dielectric interposer 1000.

In some embodiments, the terminal pad openings 1025 in the interconnectlayer 1020 provide connections for optoelectrical die 1060 to theinterconnect metal lines 1026 as shown in FIG. 10B. Interconnect metallines 1026 within interconnect layer 1020 form interconnects betweenoptoelectrical devices 1060 and optional electrical devices (not shown)mounted onto the interposer, or to form connections for one or more ofoptoelectrical devices and electrical devices connected external to theinterposer 1000.

In some embodiments, the top layer of the interconnect layer 1020 may beelectrically conductive or insulating. In preferred embodiments in whichoptical die are to be mounted onto the interposer 1000, metal traces1026 are routed within the interconnect layer 1020 that are accessiblethrough openings 1025 to provide electrical and mechanical connectionsfor the optical, electrical, and optoelectrical devices in, on, orconnected to the interposer 1000, and to the underlying electricaldevice 1064. It is to be understood that the mounting of purely opticaldie (i.e., die that have an optical function but that are notelectrical) as in a discrete waveguide for example, can benefit from themethods of mechanical attachment commonly used in the attachment ofelectrical die. Attachment of purely optical devices using electricalbond pads is within the scope of the current invention as describedherein.

In some embodiments, intermetal dielectric 1027 in the interconnectlayer 1020 provides electrical isolation for the metal interconnects1026. The interconnect layer 1020 is a structure of metal traces 1026and intermetal dielectric 1027 that provides electrically insulatedinterconnections for the optical, electrical, and optoelectrical die1060 on the dielectric interposer 1000, and in some embodiments, allowfor the interconnection of devices mounted external to the interposer1000 but for which connections are required within the interposer 1000.

Submount assembly 1005 is formed from the optical interposer 1000 by theinclusion of electrical, optical, optoelectric devices 1060 onto theinterposer 1000. FIG. 10B shows a cross sectional schematic of anembodiment of a submount assembly 1005 with optical fiber 1090positioned to provide an optical pathway between the optical fiber 1090and a waveguide fabricated from the inventive planar dielectric stack1040. FIG. 10B also shows optoelectrical device 1060 mounted to terminalpad openings 1025 in interconnect layer 1020. In some embodiments,terminal pad openings 1025 are provided through openings in the bufferlayer 1030, or another layer on the surface of the interconnect layer1020. In some embodiments, optical signals are received from opticalfiber 1090, into planar waveguides formed from the inventive dielectricstack 1040 and routed to optoelectrical or optical device 1060 forprocessing, re-routing, or conversion to electrical signals, forexample. In some embodiments, optoelectrical die 1060 are connected toone or more electrical devices 1064 via metal lines 1026 in theinterconnect layer 1020.

In other embodiments, the optical signals originate on the submountassembly 1005 and are transmitted through planar waveguides formed fromthe inventive dielectric film structure 1040 to the optical fiber 1090.In yet other embodiments, the signals are received from the opticalfiber 1090 to the submount assembly 1005 for one or more of processing,routing, and conversion to electrical signals.

Referring to FIG. 11, cross sectional schematics of embodiments of theinventive optical dielectric interposer structure 1100 and submountassembly 1105 are shown. In FIG. 11A, interposer 1100 is shown andincludes substrate 1110 and interconnect layer 1120. Interconnect layer1120 is a structure of metal traces 1126 and intermetal dielectricmaterial 1127 within which conductive pathways are provided forinterconnecting electrical and optoelectrical devices and die that areformed on, mounted in, or connected to the dielectric interposer 1100.In some embodiments, interconnected devices are interconnected to theinterposer 1100 from an external mount or submount assembly. The dottedlines in interconnect layer 1120 shown in FIG. 11A schematicallyrepresent examples of electrical pathways 1126 within the interconnectlayer 1120 for interconnecting optoelectrical devices and electricaldevices mounted to terminal pad interconnect openings 1125, for example.FIG. 11A shows inventive dielectric stack 1140 mounted via bonding pads1122 as a discrete dielectric waveguide component 1165 to interconnectlayer 1120. In some embodiments, the dielectric stack 1140 is fabricatedor formed independently of the substrate 1110 and the interconnect layer1120, and then added as a discrete element to form interposer 1100. Itis important to note that the formation of interposer 1100 may beaccomplished concurrently with the formation of submount assembly 1105for embodiments in which the discrete waveguide components 1165, withinventive dielectric stack 1140, are added to interposer 1100concurrently with optoelectrical and electrical components 1160 as shownin FIG. 11B.

In embodiments, discrete waveguide component 1165, fabricated with theinventive dielectric stack 1140, is a simple conduit for thetransmission of optical signals. In other embodiments, one or morediscrete waveguide components 1165 on submount assembly 1105 areconduits for the transmission of optical signals from an optical fiberattached to the submount assembly to one or more locations on thesubmount assembly. In yet other embodiments, discrete waveguidecomponents 1165 on submount assembly 1105 are conduits for thetransmission and distribution of optical signals from one or moreoptical fibers attached to the submount assembly to one or morelocations on the submount assembly 1105. In yet other embodiments,discrete waveguide components 1165 on submount assembly 1105 can includeone or more of a spot size converter, a filter, an arrayed waveguide, amultiplexers, a demultiplexer, a grating, a power combiner, and thelike.

In FIG. 11B, inventive planar dielectric stack structure 1140 is shownas discrete waveguide component 1145 attached to the interconnect layer1120 on substrate 1110. Submount assembly 1105 is formed from theoptical dielectric interposer 1100 by the inclusion of optical,electrical, and optoelectrical devices 1160, 1162 onto the interposer1100. FIG. 11B shows a cross sectional schematic of an embodiment of asubmount assembly 1105 with optical fiber 1190 positioned to provide anoptical pathway to the discrete dielectric waveguide component 1165. Inthe embodiment shown in FIG. 11B, the inventive planar dielectric stack1140 is a pre-fabricated discrete optical waveguide component 1165mounted to interposer 1100. FIG. 11B shows optoelectrical device 1160mounted to terminal pad openings 1125 in interconnect layer 1120 to formsubmount assembly 1105. In an embodiment, optical fiber 1190 is alignedto discrete waveguide 1165, formed from inventive dielectric stack 1140,which is further aligned to optical device 1160 to allow for thereceiving and sending of optical signals for processing, re-routing, orconversion to electrical signals, for example. Optical alignment ofdevices to the waveguide, in embodiments, provides less than 1 dB powerloss, and in preferred embodiments, less than 0.5 dB. Accurate alignmentis essential to reducing power loss to tolerable levels.

Terminal pad openings 1125 in the interconnect layer 1120 provide forconnections of optoelectrical die 1160 to the interconnect metal traces1126. In preferred embodiments in which optoelectrical die 1160 aremounted onto the interposer 1100, metal traces 1126 are routed withinthe interconnect layer 1120 to provide electrical and mechanicalconnections 1126 for optical, electrical, and optoelectrical devices in,on, or connected to the interposer 1100. In embodiments, the intermetaldielectric 1127 in the interconnect layer 1120 provides electricalisolation for the metal interconnects 1126. The interconnect layer 1120is a structure of metal lines and traces 1126 and intermetal dielectric1127 that provide interconnections for the optical, electrical, andoptoelectrical die 1160, 1162 on the dielectric interposer 1100, and insome embodiments, allow for the interconnection of devices mountedexternal to the interposer 1100 but for which connections are requiredon or within the interposer 1100.

In FIG. 11C, interposer 1100 is shown and includes substrate 1110,interconnect layer 1120, discrete waveguide component 1165, andintegrated electrical device 1164. Interconnect layer 1120 is astructure of metal lines and traces 1126 and intermetal dielectricmaterial 1127 within which conductive pathways for interconnectingelectrical and optoelectrical devices 1160, 1162 that are fabricated on,mounted in, or connected from an external submount assembly to thedielectric interposer 1100, or provided in underlying substrate 1110.The dotted lines in interconnect layer 1120 shown in FIG. 11Cschematically represent examples of electrical pathways 1126 within theinterconnect layer 1120 for interconnecting optoelectrical devices 1160and electrical devices 1162 mounted to terminal pad interconnectopenings 1125. In preferred embodiments in which optoelectrical die 1160are mounted onto the interposer 1100, metal interconnects 1126 arerouted within the interconnect layer 1120 to provide electrical andmechanical connections for electrical and optoelectrical devices in, on,or connected to the interposer 1100, and to the underlying electricaldevices 1164. Integrated electrical device 1164 in underlying substrate1110, in some embodiments, is one or more of a transistor, capacitor,resistor, inductor, or other electrical device, or array of electricaldevices. In other embodiments, integrated electrical device 1164 is ap-channel metal oxide semiconductor (PMOS) transistor or an n-channelmetal oxide semiconductor (NMOS) device, or array of one or more ofthese devices. In yet other embodiments, device 1164 is an array oftransistors based on complementary metal oxide semiconductor (CMOS)transistor technology. In yet other embodiments, the integratedelectrical device 1164 is a bipolar transistor or an array of bipolartransistor devices. In yet other embodiments, the integrated electricaldevice 1164 is a field effect transistor or an array of field effecttransistors. In some embodiments, transistor arrays 1164 in thesubstrate 1110, are used for signal processing, signal conditioning,signal generation, memory, and computation, for example.

In FIG. 11C, the inventive dielectric stack 1140 is shown in the form ofa discrete dielectric waveguide component 1165 mounted to interconnectlayer 1120 via bonding pads 1122. In some embodiments, the dielectricstack 1140 is fabricated independently of the substrate 1110 and theinterconnect layer 1120, and then added as a discrete element to forminterposer 1100 as shown, for example, in FIG. 11C. Although electricalconnections are not required for optical waveguides, bonding pads 1122,in some embodiments, are similar to bond pads used to form electricalconnections. In other embodiments, other adhesion methods are used thatinclude adhesive, epoxy, or other bonding material.

Submount assembly 1105, shown in FIG. 11D, is formed from the opticalinterposer 1100 with the inclusion of electrical, optical, optoelectricdevices on the interposer 1100. It is important to note that theformation of inventive interposer 1100 with the addition of the discretewaveguide 1165 is accomplished concurrently with the formation ofsubmount assembly 1105 for embodiments in which the discrete waveguidecomponents 1165 are added to interposer 1100 concurrently with optical,optoelectrical, and electrical components 1160. FIG. 11D shows a crosssectional schematic of an embodiment of a submount assembly 1105 withoptical fiber 1190 positioned to provide an optical pathway between theoptical fiber 1190 and a planar waveguide 1165 fabricated from theinventive planar dielectric stack 1140. FIG. 11D also showsoptoelectrical device 1160 mounted to terminal pad openings 1125 ininterconnect layer 1120. In an embodiment, optical signals are receivedfrom optical fiber 1190, into planar waveguides 1165 formed from theinventive dielectric stack 1140 and routed to optoelectrical or opticaldevice 1160 for processing, re-routing, or conversion to electricalsignals, for example. In some embodiments, optoelectrical die 1160 areconnected to one or more electrical devices 1162 and integratedelectrical devices 1164 via metal lines 1126 in the interconnect layer1120. In embodiments, optical fiber 1190 is aligned to discretewaveguide 1165, formed from inventive dielectric stack 1140, which isfurther aligned to optical device 1160 to allow for the receiving andsending of optical signals for processing, re-routing, or conversion toelectrical signals, for example. Optical alignment of devices to thewaveguide, in embodiments, provides less than 1 dB power loss and inother embodiments, less than 0.5 dB. In preferred embodiments, powerloss is much less than 0.5 dB. Accurate alignment between the opticalfiber and the discrete waveguide 1165 fabricated from the inventivedielectric stack 1140, and between the dielectric stack 1140 and theoptical or optoelectrical device 1160, is necessary to reduce potentialpower loss to tolerable levels.

In some embodiments, the optical signals originate on the submountassembly 1105 and are transmitted through planar dielectric waveguidestructure 1140 to the optical fiber 1190. In yet other embodiments, thesignals are received from the optical fiber 1190 for one or more ofprocessing, routing, and conversion to electrical signals.

Referring to FIG. 12A, the steps of forming a dielectric interposer witha patterned waveguide from the inventive dielectric stack structure areshown that include a providing step 1000, a depositing step 1210, and apatterning step 1220.

In providing step 1200, a substrate is provided with one or moreoptoelectrical or electrical devices coupled to an interconnectionlayer. In embodiments, these devices are one or more of a transistor,capacitor, resistor, inductor, or other electrical device, or an arrayof one or more electrical devices. In other embodiments, these devicesare one or more of a p-channel metal oxide semiconductor (PMOS)transistor and an n-channel metal oxide semiconductor (NMOS) device ordevices. In yet other embodiments, the devices are an array oftransistors based on complementary metal oxide semiconductor (CMOS)transistors technology. In yet other embodiments, the one or moredevices coupled to the interconnection layer as described in providingstep 1200 in FIG. 12A is a bipolar transistor, two or more bipolartransistors, or an array of bipolar transistor devices. In yet otherembodiments, the one or more devices is a field effect transistor, twoor more field effect transistors, or an array of field effecttransistors. In some embodiments, transistor arrays coupled to theinterconnect layer are used for signal processing, signal conditioning,signal generation, memory, and computation, for example.

In depositing step 1210, a stack of dielectric layers is deposited onthe substrate to form the unpatterned inventive dielectric stack on thesubstrate, which is then patterned in patterning step 1220 to form theinventive interposer. In some embodiments, the patterned dielectricstack structure can be a section of waveguide aligned to an optical orelectrical device, for example, for the transmission of optical signalsto and from an optical fiber connected to the submount assembly. Inother embodiments, these waveguides can include sections of theinventive dielectric stack that are patterned spot size converters,filters, arrayed waveguides, multiplexers, demultiplexers, gratings,power combiners, and the like. In yet other embodiments, thesewaveguides can provide part of a mechanical structure for the formationof hermetic seals. In yet other embodiments, theses waveguides can be acombination of one or more of these types of structures fabricated fromthe inventive dielectric stack structure. In yet other embodiments, thebuffer layer and the layers of the repeated stack are patterned to forma filter, an arrayed waveguide, a grating, a multiplexer, ademultiplexer, a spot size converter, or a power combiner, and the like.

In embodiments, the patterning step 1220 is used to pattern the blanketdielectric stack structures into one or more planar waveguides.Patterning steps can include the use of established photoresist layers,used either directly as a mask for wet or dry etching or etchprocessing, or via a photoresist layer used to transfer a pattern fromthe photoresist to a hard mask which is utilized for wet or dry etchingor etch patterning of the inventive dielectric film stack. Processes forphotoresist patterning and subsequent wet and dry etching of filmstructures are well established for those skilled in the art ofdielectric film patterning techniques.

Referring to FIG. 12B, steps of forming a submount assembly with theinventive interposer are shown that include providing step 1240, a firstcoupling step 1250, and a second coupling step 1260. In providing step1240, a substrate is provided wherein the substrate includes at least afirst device coupled to an interconnection layer, wherein the substrateincludes a waveguide patterned from a stack of dielectric layers.Patterned waveguide structures include filters, arrayed waveguides,gratings, multiplexers, demultiplexers, spot size converters, powercombiners, and the like. In the first coupling step 1250, a seconddevice is coupled to the substrate, wherein the device is configured tointerface between the waveguide and the at least a device. Inembodiments, the second device is a receiving device, for example, suchas a photodiode for receiving optical signals transmitted through thewaveguide and subsequently converting the optical signals to electricalsignals that are delivered to the interconnect layer. Conversely, inother embodiments, the second device is a sending device, for example,such as a laser for converting electrical signals from the interconnectlayer, for example, to optical signals for transmission to thewaveguide. In the second coupling step 1260, an optical fiber is coupledto the substrate, wherein the optical fiber is configured to interfacewith the waveguide. Optical fibers are typically used in communicationnetworks for the transmission of optical signals between submountassemblies and over long distances. By contrast, planar waveguides andthe transmission of optical signals in free space are used to transmitoptical signals within submount assemblies and over short distances.Optical fibers that are used to deliver optical signals are typicallyconnected to the substrate and aligned with waveguides or other devices,such as a lens, to provide the necessary interface for transferring theoptical signals from the fiber to the submount assembly to which theoptical fiber is connected.

Referring to FIG. 13A, a perspective view of interposer 1300 is shownfor an embodiment that includes inventive dielectric film stack 1340patterned to form a waveguide, a v-groove 1392 for coupling and aligningan optical fiber to the interposer 1300, and x-y-z stop structure 1366for aligning devices to the patterned dielectric stack 1340. In theembodiment shown in FIG. 13A, x-y-z stop structure 1366 is a singleelement. In other embodiments, any one of the x-stop, y-stop, and z stopcan be combined to facilitate the alignment of optical andoptoelectrical devices to the submount assembly. In yet otherembodiments, the x-stop, a y-stop, and a z-stop can be in one or moreindividual parts, or multiple parts, to provide the same function ofaligning devices in each of the x, y, and z directions identified inFIG. 13A. In other embodiments, one or more stops are provided for oneof the x, y, and z directions. In yet other embodiments, one or morestops are provided for two or three of the x, y, and z directions. Andin yet other embodiments, multiple stops are provided for one or more ofthe x, y, and z directions. In yet other embodiments, one or morealignment marks are provided in addition to the stops. In yet otherembodiments, alignment marks are provided to align the optical,optoelectrical, and electrical devices without the stops.

Referring to FIG. 13B, a cross sectional schematic of an embodiment forsubmount assembly 1305 is shown that is formed on interconnect layer1320 on substrate 1310 with inventive dielectric stack 1340. In theembodiment shown in FIG. 13B, features 1367, 1368, 1369 are provided forthe alignment of optical or electrical device 1360 to the planarwaveguide fabricated from the dielectric stack 1340. Optoelectricaldevice 1360 is connected through buffer layer 1330 to metal layer 1326.Metal layers 1326 are insulated with intermetal dielectric 1327 ininterconnect layer 1320. In some embodiments, interconnect metal layers1326 connect optoelectrical devices 1360 to integrated electricaldevices 1364 in the substrate 1310 or to other devices in the submountassembly 1305. Alignment of optical/optoelectronic device 1360 isrequired to align the optical sending or receiving side 1361 of opticalor optoelectrical device 1360 to the planar waveguide formed from theinventive dielectric stack structure 1340 and to thereby allow for thetransfer of optical signals between the planar waveguide formed from theinventive dielectric stack structure 1340 and the optical oroptoelectrical device 1360. It is important to note that for embodimentsin which the device 1360 is an optical device, alignment is requiredwithin the submount assembly 1305 to provide for the transfer of opticalsignals between the planar waveguides and the device 1360 in thesubmount assembly 1305, but not necessarily for electrical connections.In some embodiments, however, metal bond pads are implemented to attachoptical devices 1360. Alignment of the planar waveguides formed from theinventive dielectric stack structure 1340 to optical fiber 1390 isachieved in some preferred embodiments with v-groove 1392 in substrate1310.

In an embodiment shown in FIG. 13B, substrate 1310 is shown withoptional integrated device 1364. Integrated electrical devices 1364, inpreferred embodiments, are connected to the interconnect layer 1320.Interconnect layer 1320 is a structure of metal lines 1326 andintermetal dielectric layers 1327 that provide insulated conductivepathways for interconnecting electrical and optoelectrical devices anddies that are fabricated on, mounted in, or connected from an externalsubmount assembly to the submount assembly 1305. In preferredembodiments in which optoelectrical die 1360 are mounted onto thesubmount assembly 1305, metal interconnects 1326 are routed within theinterconnect layer 1320 to provide electrical connections for electricaland optoelectrical devices in, on, or connected to the submount assembly1305, and to the underlying electrical devices 1364.

Alignment marks 1365 are provided in some preferred embodiments for thealignment of optical, electrical, and optoelectrical devices on thesubmount assembly 1305. In some embodiments, alignment marks areprovided in the buffer layer 1330 or the top layer of the interconnectlayer 1320 of the interposer 1300 for alignment of devices, such as theoptoelectrical device 1360, within the submount assembly. Alternatively,alignment marks can be provided in other layers, on or in, thesubstrate. In preferred embodiments, alignment mark 1369 is for opticalalignment, as is used in automated die placement tools for example, toposition the die onto the submount assembly 1305. Alignment mark 1369 inembodiments is a patterned feature in or on a layer or the substrate inthe submount assembly 1305. In some embodiments, the patterned featuresare an ink mark, a coloration mark, or discoloration mark of the top oranother layer in the substrate or in one of the layers on the substrate.In some embodiments, the alignment mark is a means of providing opticalcontrast. Alignment mark 1369 in some embodiments is one or more of anetched feature, a deposited feature, a laser scribed feature, a featurecreated by exposure to an electron beam, or an ion milled feature.

Alignment features 1367 and 1368 provide physical stops for thealignment of optical die 1360, and other devices on the submountassembly 1305. Accurate placement of devices and waveguides on opticalsubmount assemblies is necessary for the transmission of the opticalsignals through the optical circuit on the submount assembly 1305. Ininstances for which optical devices and features are not aligned,significant loss of the optical signal can occur, and in extremecircumstances can result in complete loss or blockage of the opticalsignal. Stop 1368, in the embodiment shown in FIG. 13B, is a z-directionstop, in that this stop is intended to fix the height (in thez-direction) of optoelectric device 1360 on the submount assembly 1305.Stop 1367, also in the embodiment shown in FIG. 13B, is an x-directionstop, in that this stop is intended to fix the location of theoptoelectric device 1360 in the x-direction as referenced in FIG. 13A onthe submount assembly 1305. In some embodiments, a y-direction stop isalso included. And in yet other embodiments, one or more of anx-direction stop, a y-direction stop, and a z-direction stop areprovided. In yet other embodiments, one or more stops are provided foreach device 1360 mounted on the submount assembly 1305 that requiresalignment.

Additionally, in preferred embodiments, a v-groove feature 1392 or otheralignment feature is provided to align the optical fiber 1390 to thesubmount assembly 1305 and to planar waveguides formed from theinventive dielectric stack 1340.

Referring to FIG. 14, steps for forming a dielectric interposer with apatterned waveguide from the inventive dielectric stack structure areshown that include a providing step 1400, a first forming step 1410, asecond forming step 1420, and a third forming step 1430 as describedherein. In providing step 1400, a substrate is provided wherein thesubstrate includes an interconnection layer (see interconnect layer1320, for example.) In a first forming step 1410, a waveguide is formedthat includes the inventive dielectric film structure on the substrate.In a second forming step 1420, at least one of an x-stop, a y-stop, az-stop, and an alignment mark are formed on the substrate wherein thex-stop, a y-stop, a z-stop, and an alignment mark are configured toalign a device with the waveguide. In a third forming step 1430, atleast one alignment feature is formed on the substrate wherein thealignment feature is configured to align an optical fiber with thewaveguide.

A specific benefit and feature of the planar dielectric waveguidestructure is that in addition to its primary use for fabricating opticalwaveguides, it can also be used to produce mechanical features such asthe alignment stops. In some embodiments, for example, the inventivedielectric stack is patterned using photoresist, for example, and thenetched to a depth to establish the z-direction height, and for example,to create features for x-direction and y-direction stops as required.The capability to produce stops from the dielectric stack material,outside of the waveguide areas, provides an added benefit inimplementing the planar dielectric stack structure on the inventiveinterposer. The use of the dielectric stack film stack to producemechanical features such as the structures described for alignment stopsand marks, as well other features described herein, is particularlyenabled by the achievable thickness ranges of the inventive dielectricstacks. Thicknesses on the order of 2-25 micrometers are of the samethickness ranges that are suitable for alignment marks and stops. Bycombining the highly accurate vertical dimensioning capability that isachievable with highly controllable additive deposition technology withthe highly controllable subtractive dry and wet etch technology, therelative heights of alignment features and stop features formed from thedielectric stack film structures can be formed with high accuracy. Inaddition to the applicable thickness benefits, the accuracy in thelateral dimensioning of the stops is generally provided byphotolithographic patterning processes, which are highly accurate towithin small fractions of a micrometer.

Referring to FIG. 15A, submount assembly 1505, formed from interposer1500, is shown that includes substrate 1510, interconnect layer 1520,and inventive dielectric stack 1540. Dielectric stack 1540 is patternedto form inventive planar dielectric waveguide. Interconnect layer 1520is a structure of metal lines 1526 and intermetal dielectric 1527. Metallines 1526 provide electrically conductive pathways for interconnectingelectrical and optoelectrical devices and dies that are fabricated on,mounted in, or connected from an external submount assembly to thedielectric interposer 1500. In a preferred embodiment, one or moreoptoelectrical die 1560 are mounted onto the interposer 1500, and themetal interconnects 1526 are routed within the interconnect layer 1520to provide electrical connections for electrical and optoelectricaldevices in, on, or connected to the interposer 1500, or submountassembly 1505, and to underlying integrated electrical devices in thesubstrate, if present. It is to be understood that optical devices canbe mounted with metal bond pads 1522, as means for mechanical bonding,without the specific requirement for electrical connections to otherdevices on the submount assembly 1505. A discrete waveguide (see 1140,for example) may not require electrical interconnection to other deviceson the submount assembly 1505, but the same or similar bondingmethodologies that are used for to provide mechanical bonding andelectrical interconnection can be utilized to bond the optical device1560 to the submount assembly 1505.

In optical circuits, and in particular, in optical circuits within whichlasers are utilized for converting electrical signals to opticalsignals, significant levels of heat can be generated that may requiredissipation in some embodiments to prevent premature failure of, ordamage to, a submount assembly or components mounted on the submountassembly. In addition to lasers, other optical, electrical, andoptoelectrical devices can generate significant levels of heat while inoperation. Submount assemblies, therefore, in some embodiments, wouldbenefit from design features that facilitate heat dissipation. In theinventive submount assembly 1505, one or more of a thermally conductivedielectric layer is incorporated into the inventive submount assembly1505 with the inventive dielectric stack 1540 to facilitate dissipationof thermal energy from the submount assembly 1505.

In the cross section shown in FIG. 15A of an embodiment for theinventive submount assembly 1505, a thermally conductive dielectriclayer 1528 is disposed between the substrate 1510 and the interconnectlayer 1520. In these and other embodiments, the thermally conductivedielectric material, such as aluminum nitride, for example, is combinedwith inventive submount assembly 1505 in conjunction with heatgenerating optoelectrical devices 1560 and inventive planar dielectricstack 1540. In embodiments, inclusion of heat-dissipating, thermallyconductive dielectric layer 1528 with inventive dielectric stackstructure 1540 improves the reliability of the submount assembly 1505 byproviding thermally conductive pathways that allow for the transferringof heat from heat generating devices 1560 to heat sinks connected to thesubstrate 1510 or the submount assembly 1505. In preferred embodiments,thermally conductive dielectric layer 1528 is aluminum nitride or analloy of aluminum nitride. In other embodiments, other thermallyconductive dielectric material is used in submount assembly 1505 inconjunction with the optoelectrical devices 1560 and inventive planardielectric stack 1540. In other embodiments, materials that areelectrically conductive, such as the metal traces 1526 that are used inthe interconnect layer 1520, are used to transfer heat from heatgenerating devices 1560 to the thermally conductive layers 1528 forconduction of heat to heat sinks on the submount assembly 1505.

In other embodiments, as for example shown in FIG. 15B, a thermallyconductive dielectric layer 1529 is positioned within the interconnectlayer 1520. The metal traces 1526 in interconnect layer 1520, which arecommonly composed of aluminum, copper, other metal, or combination ofmetals, generally have a high thermal conductivity, and can provide heatdissipation pathways from the heat generating optoelectronic device 1560to the thermally conductive dielectric material 1529. The thermallyconductive dielectric material 1529 is used in some embodiments toprovide pathways that allow for the transferring of heat from the heatgenerating devices 1560 to one or more heat sinks connected to thesubmount assembly 1505.

Referring to FIG. 16A, a sequence of steps for forming a substrate witha thermally conductive layer and an interconnection layer used inembodiments of the inventive dielectric interposer 1500 is shown. Thesesteps, which include the formation of a thermally conductive layer areshown that include a providing step 1600, a first forming step 1610, anda second forming step 1620, as described herein. In providing step 1600,a substrate is provided whereon a thermally conductive layer is formedin first forming step 1610. In the second forming step 1620, aninterconnection layer is formed on the thermally conductive layer. Thesequence of steps shown in FIG. 16A is one method for preparing asubstrate with a thermal layer 1580 and an interconnect layer 1520 inpreparation for the deposition of the inventive dielectric stack 1540,and the resulting formation of the inventive dielectric interposer 1500.In embodiments, the thermal layer 1528 is a heat sink for the removal ofexcess heat from devices 1560, for example. In other embodiments, thethermal layer 1528 provides a thermally conductive pathway for thetransfer of heat from heat-generating devices 1560 to heat sinks on orconnected in some way to the sub-mount assembly 1505.

In FIG. 16B, steps for forming other embodiments of the inventivedielectric interposer 1500 with a thermally conductive dielectric layerare shown. The steps in FIG. 16B include a providing step 1640, a firstforming step 1650, a second forming step 1660, and a third forming step1670. In providing step 1640, a substrate 1510 is provided for thedielectric interposer 1500. In first forming step 1650, a whole or partof an interconnect layer is formed on the substrate 1510. In someembodiments, first forming step 1650 includes the formation of a part ofthe interconnect layer, that is, one or more layers of the interconnectlayer 1520 but not the complete thickness of the interconnect layer. Inother embodiments the thermally conductive dielectric layer 1529 isformed on the interconnect layer 1520. It is important to note that thethermally conductive layer can be formed at one or more of variouspositions in the interposer structure 1500 and remain within the scopeof the current invention. Embodiments for the thermally conductivedielectric layer, for the purposes of providing a heat sink or a pathwayto a heat sink include one or more of a thermally conductive layer 1528on the substrate 1510, a thermally conductive layer 1529 on theinterconnect layer 1520, and a thermally conductive layer 1529 withinthe interconnect layer 1520, as described herein. The thermallyconductive layer, in some embodiments, is partially at one height in theinterconnect layer 1520, and is partially at one or more other heightsin the interconnect layer 1520. For example, a thermally conductivelayer 1528 may be on the substrate 1510 for part of the submountassembly 1505 and then partially at another height within theinterconnect layer 1520. In these embodiments, connections between thelevels of the thermally conductive layers can be provided using the samethermally conductive material as in the thermally conductive layers1529, a metal layer 1526, or an intermetal dielectric 1527. In preferredembodiments, the use of the same thermally conductive material toconnect multiple thermally conductive layers 1528, 1529 is expected toproduce the most efficient heat transfer although this approach mightalso have increased processing costs in some embodiments.

The second forming step 1660, for embodiments in which the thermallyconductive layer 1529 is formed within the interconnect layer 1520, istypically followed by completion of the remaining layers of theinterconnect layer 1520. In these embodiments, electrical connections1526 may be required in some embodiments through the thermallyconductive dielectric layer 1529 to connect underlying integratedelectrical devices (see integrated device 964, for example) or toconnect underlying connection layers 1526 that reside below thethermally conductive layer 1529. Third forming step 1670 includes theforming of an electrical connection in or through the dielectric layerthat contains a thermally conductive dielectric layer 1529 to one ormore of the interconnection layers 1526 that reside in the dielectriclayer and in some embodiments to underlying integrated electricaldevices (see integrated electrical device 964, for example). Similarly,for embodiments in which the thermally conductive layer 1529 isdeposited on the complete, or partially completed, interconnect layer1520, third forming step 1670 also includes the forming of electricalconnections 1526 through the thermally conductive dielectric layer 1529and the forming of one or more connections in or through this thermallyconductive layer 1529 to one or more of the interconnection layers 1526that reside below the thermally conductive dielectric layer 1529. Inembodiments in which the interconnect layer 1520 is nearly completed,the thermally conductive layer 1529 may form the uppermost dielectriclayer in the structure of the interconnect layer 1520.

It is important to note that the thermally conductive layer 1528, 1529can be incorporated into the inventive interposer 1500 in various waysand remain within the scope of the current invention. FIG. 16B showssteps in the formation of some embodiments of the inventive dielectricinterposer 1500 with the inventive dielectric stack 1540 for which athermally conductive dielectric layer 1528, 1529 is included asdescribed herein. In embodiments, the thermally conductive dielectriclayer 1528, 1529 is one or more of a heat sink for the removal of excessheat from devices 1560, for example, and a thermally conductive pathwayfor the transfer of heat from heat-generating devices 1560 to heat sinkson or connected to the sub-mount assembly 1505. The combination ofheat-removing layers 1528, 1529 with the heat generating devices 1560and integrated planar dielectric waveguides formed from the inventivedielectric stack structure 1540 are beneficial for enhancing thereliability of submount assemblies that are uniquely enabled by thiscombination.

Referring to FIG. 17A, a cross sectional schematic of an unpatternedinventive dielectric stack 1740 is shown for embodiments of theinventive dielectric interposer 1700 formed on substrate 1710 forembodiments with optional thermally conductive layer 1728, interconnectlayer 1720, and buffer layer 1730. Patterning of inventive dielectricstack 1740 from FIG. 17A yields inventive dielectric stack section 1740a and inventive dielectric stack section 1740 b as shown in thecross-sectional schematic in FIG. 17B. In preferred embodiments,dielectric stack section 1740 a and dielectric stack section 1740 b formcavity 1794. The inset in FIG. 17B shows a perspective view of the topsurface of inventive interposer 1700 after patterning of the dielectricstack 1740 to form dielectric stack sections 1740 a, 1740 b, and thecavity 1746.

Referring to FIG. 17C, a schematic cross section of inventive dielectricinterposer 1705 is shown with optoelectrical device 1760 within cavity1794. In some embodiments, the optoelectrical device 1760 is connectedwith bond pad 1722 to the underlying metallization 1726 in theinterconnect layer 1720 through openings in buffer layer 1730.Metallization traces 1726 generally form interconnections between thevarious electrical devices on and within the interposer and are shownfor general demonstrative purposes in FIG. 17, and in other figures, andnot intended to show a specific patterns or structures for theinterconnections. Metallization layers 1726 provide interconnectionsbetween electrical and optoelectrical devices mounted onto theinterposer 1700, to integrated electrical devices in the substrate (seeintegrated electrical device 964, for example), and to other devices andother submount assemblies connected to submount assembly 1705.

In FIG. 17D, a cross sectional schematic of cap 1796 on submountassembly 1705 to create capped optoelectronic package 1708 is shown. Insome embodiments, cap 1796 is provided to seal the cavity 1794, and toprovide hermetically sealed protection of the submount assembly withinthe cavity 1794. Cap 1796 is coupled to the cavity walls formed fromdielectric stack sections 1740 a, 1740 b, formed from the inventivedielectric stack structure 1740, to cover and protect the optoelectricdevices 1760 mounted within the cavity 1746. In typical preferredembodiments, a metal seal 1797 is utilized to bond the cap 1796 to thecavity walls 1740 a, 1740 b. In other embodiments, the seal or bondlayer 1797 between the cap 1796 and the mechanical supports can be madefrom materials such as adhesive resins, solder material, and the like.The cap 1796 is shown mounted directly on the inventive dielectric stackstructure 1740, but it should be understood that additional layers canbe formed above the dielectric stack structure 1740 for various reasonsthat include one or more of improved bonding layer adhesion, verticalheight adjustment, alignment, and provision for positional stops, amongother reasons, and remain within the scope of the current invention.

In FIG. 18, the steps for providing a capped submount assembly 1708 frominventive submount assembly 1705 using inventive dielectric stackstructure 1740 are shown and include a providing step 1800, a firstforming step 1810, a first patterning step 1820, a second forming step1830, and a third forming step 1840 as described herein for someembodiments. In the providing step 1800, a substrate 1710 that includesan interconnection layer 1720 is provided. In some embodiments, thesubstrate 1710 has a thermally conductive layer 1728 on substrate 1710or within the interconnect layer 1720. In some other embodiments, thesubstrate 1710 does not have a thermally conductive layer 1728 on or insubstrate 1710, or on or within the interconnect layer 1720. In a firstforming step 1810, inventive dielectric stack 1740 is deposited onto theinterconnect layer 1720. Inventive dielectric stack 1740 is patterned infirst patterning step 1820 to form a waveguide from the inventivedielectric stack 1740 and one or more support structures 1740 a and 1740b that are also formed from the inventive dielectric stack 1740. Anembodiment of support structures is shown for example in FIGS. 17B-D. Ina second forming step 1830, a device 1760, for example, is formed on thesubstrate, wherein the device is configured to couple to the waveguideformed from the dielectric stack 1740. In the third forming step 1840, acap 1796 is positioned to cover the device that is coupled to thewaveguide, by disposing the cap 1796 on the dielectric stack structure1740 patterned to form a waveguide 1740 a, which also serves as amechanical support structure, and the support structures 1740 b. Thebenefit of using the inventive dielectric stack as both a mechanicalsupport and a waveguide enables the use of the waveguide to transmitlight signals into the cavity and out from devices mounted within thecavity while providing a capability for hermetic sealing. Thetransmission of light through planar waveguides formed from theinventive dielectric film structures 1740 can be used to facilitate thetransmission or receiving, or both, of optical signals from opticalfibers mounted external to the cavity, through the cavity walls 1740 a,to or from devices 1760 mounted within the cavity 1794.

In the cross sections of the embodiments for the inventive interposersand submount assemblies shown and described herein, it should beunderstood that waveguides fabricated from inventive dielectric stack140, 740, 940, 1040, and 1140, in some embodiments can be a smallsection of waveguide aligned to an optical or electrical device, forexample, for the transmission of optical signals to and from an opticalfiber connected to the submount assembly. In other embodiments, thesewaveguides can include sections of the inventive dielectric stack 140that are patterned spot size converters, filters, arrayed waveguides,multiplexers, demultiplexers, gratings, power combiners, and the like.In yet other embodiments, these waveguides can provide part of amechanical structure for the formation of hermetic seals. In yet otherembodiments, theses waveguides can be a combination of one or more ofthese types of structures fabricated from the inventive dielectric stackstructure 140. In yet other embodiments, the buffer layer and the layersof the repeated stack are patterned to form a filter, an arrayedwaveguide, a grating, a multiplexer, a demultiplexer, a spot sizeconverter, or a power combiner.

The foregoing disclosure of the exemplary embodiments of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many variations andmodifications of the embodiments described herein will be apparent toone of ordinary skill in the art in light of the above disclosure. Thescope of the invention is to be defined only by the claims appendedhereto, and by their equivalents.

Further, in describing representative embodiments of the presentinvention, the specification may have presented the method and/orprocess of the present invention as a particular sequence of steps.However, to the extent that the method or process does not rely on theparticular order of steps set forth herein, the method or process shouldnot be limited to the particular sequence of steps described. As one ofordinary skill in the art would appreciate, other sequences of steps maybe possible. Therefore, the particular order of the steps set forth inthe specification should not be construed as limitations on the claims.In addition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and remain within the spiritand scope of the present invention.

The invention claimed is:
 1. A method comprising forming multiple layersof films on a substrate, wherein the multiple layers of films comprisesa stack of silicon oxynitride films, wherein at least a siliconoxynitride film in the stack of silicon oxynitride films is formed by aplasma enhanced chemical vapor deposition (PECVD) process, whereinprocess gases in the PECVD process are configured to form the at least asilicon oxynitride film having a stress level less than 20 MPa inmagnitude; patterning the multiple layers of films to form a waveguidewith the stack of films being a core of the waveguide.
 2. A method as inclaim 1 wherein the silicon oxynitride films in the stack of siliconoxynitride films are formed by a PECVD process, wherein the siliconoxynitride films in the stack of silicon oxynitride films have a stresslevel less than 20 MPa in magnitude.
 3. A method as in claim 1 whereinthe multiple layers of films are configured to form a waveguide having astress level less than 20 MPa in magnitude.
 4. A method as in claim 1wherein the waveguide further comprises a buffer layer and a lowercladding layer under the waveguide core, and an upper cladding layerabove the waveguide core.
 5. A method as in claim 1 wherein the stresslevel of less than 20 MPa in magnitude of the at least a siliconoxynitride film is achieved by forming formed the at least a siliconoxynitride film having an index of refraction between 1.6 and 2.05.
 6. Amethod comprising forming multiple layers of films on a substrate,wherein the multiple layers of films comprises a stack of siliconoxynitride films; patterning the multiple layers of films to form awaveguide with the stack of films being a core of the waveguide, whereinat least a silicon oxynitride film in the stack of silicon oxynitridefilms is formed by a plasma enhanced chemical vapor deposition (PECVD)process, wherein process gases in the PECVD process comprise an amountof hydrogen configured to form the at least a silicon oxynitride filmusing process temperatures less than 400 C to prevent damages to thesubstrate.
 7. A method as in claim 6 wherein at least two siliconoxynitride films in the stack of silicon oxynitride films are formed bya PECVD process using different ratios of process gases, wherein processgases used in the PECVD processes comprise an amount of hydrogenconfigured to form the waveguide using process temperatures less than400 C.
 8. A method as in claim 6 wherein the silicon oxynitride films inthe stack of silicon oxynitride films are formed by PECVD processes,wherein process gases used in the PECVD processes comprise an amount ofhydrogen configured to form the waveguide using process temperaturesless than 400 C.
 9. A method as in claim 6 wherein the waveguide isformed using process temperatures less than 400 C to prevent damages tothe substrate.
 10. A method as in claim 6 wherein process gases used inthe PECVD process comprises 10% or less of hydrogen.
 11. A method as inclaim 6 wherein the process gases comprises a precursor for silicon, aprecursor for nitrogen, and a precursor for oxygen, wherein at least oneof the oxygen precursor and the nitrogen precursor comprises ahydrogen-free chemistry.
 12. A method as in claim 6 wherein the processgases comprises a precursor for silicon and one or more precursors fornitrogen and oxygen, wherein at least one of the one or more precursorsfor nitrogen and oxygen comprises a hydrogen-free chemistry.
 13. Amethod as in claim 6 wherein ratios of process gases are configured toachieve a stoichiometry for the silicon oxynitride films that exhibitsan index of refraction between 1.6 and 2.05.
 14. A method as in claim 6wherein ratios of process gases are configured to achieve a stress levelless than 20 MPa in magnitude.
 15. A method comprising forming multiplelayers of films on a substrate, wherein the multiple layers of filmscomprises a stack of silicon oxynitride films, wherein at least asilicon oxynitride film in the stack of silicon oxynitride films isformed by a plasma enhanced chemical vapor deposition (PECVD) process,wherein process gases in the PECVD process comprise a silicon precursorand one or more precursors for oxygen and nitrogen, wherein theprecursors of silicon, oxygen, and nitrogen are configured to form theat least a silicon oxynitride film, wherein the one or more precursorsof oxygen and nitrogen comprise a hydrogen-free chemistry; patterningthe stack to form a core of a waveguide.
 16. A method as in claim 15wherein the one or more precursors of oxygen and nitrogen comprise aprecursor for oxygen and a precursor for nitrogen, or a precursorcontaining oxygen and a precursor containing oxygen and nitrogen.
 17. Amethod as in claim 15 wherein the process gases used in the PECVDprocess do not include hydrogen gas, hydrogen gas mixture, or ammonia.18. A method as in claim 15 wherein the hydrogen-free chemistrycomprises oxygen, nitrous oxide, and nitrogen.
 19. A method as in claim15 wherein the hydrogen-free chemistry is configured to form thewaveguide at a temperature of 300° C. or lower.
 20. A method as in claim15 wherein ratios of process gases are configured to achieve a stresslevel less than 20 MPa in magnitude for the at least a siliconoxynitride film.